Update OpenIddictParameter to offer ImmutableArray<string> conversions instead of string[] and clone JsonNode objects to guarantee immutability

Directory.Build.targets

@@ -100,6 +100,8 @@
   <PropertyGroup
     Condition=" '$(TargetFrameworkIdentifier)' == '.NETCoreApp' And $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '9.0')) ">
     <DefineConstants>$(DefineConstants);SUPPORTS_CERTIFICATE_LOADER</DefineConstants>
+    <DefineConstants>$(DefineConstants);SUPPORTS_JSON_ELEMENT_DEEP_EQUALS</DefineConstants>
+    <DefineConstants>$(DefineConstants);SUPPORTS_JSON_ELEMENT_PROPERTY_COUNT</DefineConstants>
   </PropertyGroup>
 
   <PropertyGroup

src/OpenIddict.Abstractions/Primitives/OpenIddictExtensions.cs

@@ -639,14 +639,14 @@ public static class OpenIddictExtensions
     /// </summary>
     /// <param name="identity">The identity.</param>
     /// <returns>The destinations, returned as a flattened dictionary.</returns>
-    public static ImmutableDictionary<string, string[]> GetDestinations(this ClaimsIdentity identity)
+    public static ImmutableDictionary<string, ImmutableArray<string>> GetDestinations(this ClaimsIdentity identity)
     {
         if (identity is null)
         {
             throw new ArgumentNullException(nameof(identity));
         }
 
-        var builder = ImmutableDictionary.CreateBuilder<string, string[]>(StringComparer.Ordinal);
+        var builder = ImmutableDictionary.CreateBuilder<string, ImmutableArray<string>>(StringComparer.Ordinal);
 
         foreach (var group in identity.Claims.GroupBy(claim => claim.Type))
         {
@@ -676,14 +676,14 @@ public static class OpenIddictExtensions
     /// </summary>
     /// <param name="principal">The principal.</param>
     /// <returns>The destinations, returned as a flattened dictionary.</returns>
-    public static ImmutableDictionary<string, string[]> GetDestinations(this ClaimsPrincipal principal)
+    public static ImmutableDictionary<string, ImmutableArray<string>> GetDestinations(this ClaimsPrincipal principal)
     {
         if (principal is null)
         {
             throw new ArgumentNullException(nameof(principal));
         }
 
-        var builder = ImmutableDictionary.CreateBuilder<string, string[]>(StringComparer.Ordinal);
+        var builder = ImmutableDictionary.CreateBuilder<string, ImmutableArray<string>>(StringComparer.Ordinal);
 
         foreach (var group in principal.Claims.GroupBy(claim => claim.Type))
         {
@@ -714,7 +714,8 @@ public static class OpenIddictExtensions
     /// <param name="identity">The identity.</param>
     /// <param name="destinations">The destinations, as a flattened dictionary.</param>
     /// <returns>The identity.</returns>
-    public static ClaimsIdentity SetDestinations(this ClaimsIdentity identity, ImmutableDictionary<string, string[]> destinations)
+    public static ClaimsIdentity SetDestinations(this ClaimsIdentity identity,
+        ImmutableDictionary<string, ImmutableArray<string>> destinations)
     {
         if (identity is null)
         {
@@ -743,7 +744,8 @@ public static class OpenIddictExtensions
     /// <param name="principal">The principal.</param>
     /// <param name="destinations">The destinations, as a flattened dictionary.</param>
     /// <returns>The principal.</returns>
-    public static ClaimsPrincipal SetDestinations(this ClaimsPrincipal principal, ImmutableDictionary<string, string[]> destinations)
+    public static ClaimsPrincipal SetDestinations(this ClaimsPrincipal principal,
+        ImmutableDictionary<string, ImmutableArray<string>> destinations)
     {
         if (principal is null)
         {

src/OpenIddict.Abstractions/Primitives/OpenIddictMessage.cs

@@ -4,9 +4,11 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Collections.ObjectModel;
 using System.Collections.Specialized;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 using System.Text;
 using System.Text.Encodings.Web;
 using System.Text.Json;
@@ -141,17 +143,15 @@ public class OpenIddictMessage
                 continue;
             }
 
-            var values = parameter.Select(parameter => parameter.Value).ToArray();
-
             // Note: the core OAuth 2.0 specification requires that request parameters
             // not be present more than once but derived specifications like the
             // token exchange specification deliberately allow specifying multiple
             // parameters with the same name to represent a multi-valued parameter.
-            AddParameter(parameter.Key, values.Length switch
+            AddParameter(parameter.Key, parameter.Select(parameter => parameter.Value).ToArray() switch
             {
-                0 => default,
-                1 => values[0],
-                _ => values
+                      []       => default,
+                [string value] => new OpenIddictParameter(value),
+                 [..] values   => new(ImmutableCollectionsMarshal.AsImmutableArray(values))
             });
         }
     }
@@ -161,7 +161,7 @@ public class OpenIddictMessage
     /// </summary>
     /// <param name="parameters">The message parameters.</param>
     /// <remarks>Parameters with a null or empty key are always ignored.</remarks>
-    public OpenIddictMessage(IEnumerable<KeyValuePair<string, string?[]?>> parameters)
+    public OpenIddictMessage(IEnumerable<KeyValuePair<string, ImmutableArray<string?>?>> parameters)
     {
         if (parameters is null)
         {
@@ -180,11 +180,11 @@ public class OpenIddictMessage
             // not be present more than once but derived specifications like the
             // token exchange specification deliberately allow specifying multiple
             // parameters with the same name to represent a multi-valued parameter.
-            AddParameter(parameter.Key, parameter.Value?.Length switch
+            AddParameter(parameter.Key, parameter.Value switch
             {
-                null or 0 => default,
-                1         => parameter.Value[0],
-                _         => parameter.Value
+                   null or []  => default,
+                [string value] => new OpenIddictParameter(value),
+                 [..] values   => new OpenIddictParameter(values)
             });
         }
     }
@@ -213,11 +213,11 @@ public class OpenIddictMessage
             // not be present more than once but derived specifications like the
             // token exchange specification deliberately allow specifying multiple
             // parameters with the same name to represent a multi-valued parameter.
-            AddParameter(parameter.Key, parameter.Value.Count switch
+            AddParameter(parameter.Key, parameter.Value switch
             {
-                0 => default,
-                1 => parameter.Value[0],
-                _ => parameter.Value.ToArray()
+                      []       => default,
+                [string value] => new OpenIddictParameter(value),
+                 [..] values   => new(ImmutableCollectionsMarshal.AsImmutableArray(values.ToArray()))
             });
         }
     }
@@ -243,17 +243,15 @@ public class OpenIddictMessage
                 continue;
             }
 
-            var values = parameters.GetValues(name);
-
             // Note: the core OAuth 2.0 specification requires that request parameters
             // not be present more than once but derived specifications like the
             // token exchange specification deliberately allow specifying multiple
             // parameters with the same name to represent a multi-valued parameter.
-            AddParameter(name, values?.Length switch
+            AddParameter(name, parameters.GetValues(name) switch
             {
-                null or 0 => default,
-                1         => values[0],
-                _         => values
+                  null or []   => default,
+                [string value] => new OpenIddictParameter(value),
+                 [..] values   => new(ImmutableCollectionsMarshal.AsImmutableArray<string?>(values))
             });
         }
     }

src/OpenIddict.Abstractions/Primitives/OpenIddictParameter.cs

@@ -8,64 +8,88 @@ using System.Collections.Immutable;
 using System.ComponentModel;
 using System.Globalization;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using System.Text.Json;
 using System.Text.Json.Nodes;
+using Microsoft.Extensions.Primitives;
 
 namespace OpenIddict.Abstractions;
 
 /// <summary>
-/// Represents an OpenIddict parameter value, that can be either a primitive value,
-/// an array of strings or a complex JSON representation containing child nodes.
+/// Represents an OpenIddict parameter value and provides two-way conversion operators that allow
+/// representing it as a primitive value, an immutable array of strings or a JSON element or node.
 /// </summary>
 public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
 {
+    private readonly object? _value;
+
     /// <summary>
     /// Initializes a new parameter using the specified value.
     /// </summary>
     /// <param name="value">The parameter value.</param>
-    public OpenIddictParameter(bool value) => Value = value;
+    public OpenIddictParameter(bool value) => _value = value;
 
     /// <summary>
     /// Initializes a new parameter using the specified value.
     /// </summary>
     /// <param name="value">The parameter value.</param>
-    public OpenIddictParameter(bool? value) => Value = value;
+    public OpenIddictParameter(bool? value) => _value = value;
 
     /// <summary>
     /// Initializes a new parameter using the specified value.
     /// </summary>
     /// <param name="value">The parameter value.</param>
-    public OpenIddictParameter(JsonElement value) => Value = value;
+    public OpenIddictParameter(JsonElement value) => _value = value;
 
     /// <summary>
     /// Initializes a new parameter using the specified value.
     /// </summary>
     /// <param name="value">The parameter value.</param>
-    public OpenIddictParameter(JsonNode? value) => Value = value;
+    public OpenIddictParameter(JsonNode? value) => _value = value switch
+    {
+        // Clone the node to ensure the stored value cannot be mutated.
+        JsonNode node => node.DeepClone(),
+
+        null => null
+    };
 
     /// <summary>
     /// Initializes a new parameter using the specified value.
     /// </summary>
     /// <param name="value">The parameter value.</param>
-    public OpenIddictParameter(long value) => Value = value;
+    public OpenIddictParameter(long value) => _value = value;
 
     /// <summary>
     /// Initializes a new parameter using the specified value.
     /// </summary>
     /// <param name="value">The parameter value.</param>
-    public OpenIddictParameter(long? value) => Value = value;
+    public OpenIddictParameter(long? value) => _value = value;
 
     /// <summary>
     /// Initializes a new parameter using the specified value.
     /// </summary>
     /// <param name="value">The parameter value.</param>
-    public OpenIddictParameter(string? value) => Value = value;
+    public OpenIddictParameter(string? value) => _value = value;
 
     /// <summary>
     /// Initializes a new parameter using the specified value.
     /// </summary>
     /// <param name="value">The parameter value.</param>
-    public OpenIddictParameter(string?[]? value) => Value = value;
+    public OpenIddictParameter(ImmutableArray<string?> value)
+        // Note: to avoid boxing, the underlying array is directly stored as the backing value.
+        => _value = ImmutableCollectionsMarshal.AsArray(value);
+
+    /// <summary>
+    /// Initializes a new parameter using the specified value.
+    /// </summary>
+    /// <param name="value">The parameter value.</param>
+    public OpenIddictParameter(ImmutableArray<string?>? value) => _value = value switch
+    {
+        // Note: to avoid boxing, the underlying array is directly stored as the backing value.
+        ImmutableArray<string?> array => ImmutableCollectionsMarshal.AsArray(array),
+
+        null => null
+    };
 
     /// <summary>
     /// Gets the child item corresponding to the specified index.
@@ -89,9 +113,9 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     {
         get
         {
-            return Value switch
+            return _value switch
             {
-                // If the parameter is a primitive array of strings, return its length.
+                // If the parameter is an array of strings, return its length.
                 string?[] value => value.Length,
 
                 // If the parameter is a JSON array or a JSON object, return its length.
@@ -135,6 +159,9 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
                         return element.GetArrayLength();
 
                     case JsonValueKind.Object:
+#if SUPPORTS_JSON_ELEMENT_PROPERTY_COUNT
+                        return element.GetPropertyCount();
+#else
                         var count = 0;
 
                         using (var enumerator = element.EnumerateObject())
@@ -149,6 +176,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
                         }
 
                         return count;
+#endif
 
                     default: return 0;
                 }
@@ -157,11 +185,20 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     }
 
     /// <summary>
-    /// Gets the associated value, that can be either a primitive CLR type
-    /// (e.g bool, string, long), an array of strings or a complex JSON object.
+    /// Gets the associated raw value, that can be either a primitive CLR type
+    /// (e.g bool, string, long), an immutable array of strings or a complex JSON object.
     /// </summary>
-    [EditorBrowsable(EditorBrowsableState.Advanced)]
-    public object? Value { get; }
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    public object? GetRawValue() => _value switch
+    {
+        // If the value is backed by an array of strings or a JSON node, return a copy instead of the
+        // real instance to ensure mutations made on the returned object don't affect the stored array.
+        string?[] array => ImmutableArray.Create(array),
+        JsonNode node   => node.DeepClone(),
+
+        object value => value,
+        null         => null
+    };
 
     /// <summary>
     /// Determines whether the current <see cref="OpenIddictParameter"/>
@@ -174,7 +211,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// </returns>
     public bool Equals(OpenIddictParameter other)
     {
-        return (left: Value, right: other.Value) switch
+        return (_value, other._value) switch
         {
             // If the two parameters reference the same instance, return true.
             //
@@ -207,6 +244,9 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
             // If the two parameters are JsonElement instances, use the custom comparer.
             (JsonElement left, JsonElement right) => DeepEquals(left, right),
 
+            // If the two parameters are JsonNode instances, use JsonNode.DeepEquals().
+            (JsonNode left, JsonNode right) => JsonNode.DeepEquals(left, right),
+
             // When one of the parameters is a JsonElement, compare their underlying values.
             (JsonElement { ValueKind: JsonValueKind.True }, bool right) => right,
             (bool left, JsonElement { ValueKind: JsonValueKind.True })  => left,
@@ -252,8 +292,9 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
 
         static bool DeepEquals(JsonElement left, JsonElement right)
         {
+#if !SUPPORTS_JSON_ELEMENT_DEEP_EQUALS
             RuntimeHelpers.EnsureSufficientExecutionStack();
-
+#endif
             switch ((left.ValueKind, right.ValueKind))
             {
                 case (JsonValueKind.Undefined, JsonValueKind.Undefined):
@@ -267,6 +308,9 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
                 case (JsonValueKind.Null, JsonValueKind.Undefined):
                     return true;
 
+#if SUPPORTS_JSON_ELEMENT_DEEP_EQUALS
+                default: return JsonElement.DeepEquals(left, right);
+#else
                 case (JsonValueKind.Number, JsonValueKind.Number):
                     return string.Equals(left.GetRawText(), right.GetRawText(), StringComparison.Ordinal);
 
@@ -312,6 +356,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
                 }
 
                 default: return false;
+#endif
             }
         }
     }
@@ -333,7 +378,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// <returns>The hash code for the current instance.</returns>
     public override int GetHashCode()
     {
-        return Value switch
+        return _value switch
         {
             // When the parameter value is null, return 0.
             null => 0,
@@ -460,7 +505,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// <returns>A dictionary of all the parameters associated with the current instance.</returns>
     public IReadOnlyDictionary<string, OpenIddictParameter> GetNamedParameters()
     {
-        return Value switch
+        return _value switch
         {
             // When the parameter is a JsonElement representing an object, return the requested item.
             JsonElement { ValueKind: JsonValueKind.Object } value => GetParametersFromJsonElement(value),
@@ -510,7 +555,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// <returns>An enumeration of all the unnamed parameters associated with the current instance.</returns>
     public IReadOnlyList<OpenIddictParameter> GetUnnamedParameters()
     {
-        return Value switch
+        return _value switch
         {
             // When the parameter is an array of strings, return its items.
             string?[] value => GetParametersFromArray(value),
@@ -573,7 +618,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// Returns the <see cref="string"/> representation of the current instance.
     /// </summary>
     /// <returns>The <see cref="string"/> representation associated with the parameter value.</returns>
-    public override string? ToString() => Value switch
+    public override string? ToString() => _value switch
     {
         null => string.Empty,
 
@@ -633,7 +678,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
             throw new ArgumentException(SR.GetResourceString(SR.ID0192), nameof(name));
         }
 
-        var result = Value switch
+        var result = _value switch
         {
             // When the parameter is a JsonElement representing an array, return the requested item.
             JsonElement { ValueKind: JsonValueKind.Object } element =>
@@ -669,7 +714,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
             throw new ArgumentOutOfRangeException(nameof(index), SR.GetResourceString(SR.ID0193));
         }
 
-        var result = Value switch
+        var result = _value switch
         {
             // When the parameter is an array of strings, return the requested item.
             string?[] array => index < array.Length ? new(array[index]) : null,
@@ -706,7 +751,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
             throw new ArgumentNullException(nameof(writer));
         }
 
-        switch (Value)
+        switch (_value)
         {
             // Note: undefined JsonElement values are assimilated to null values.
             case null:
@@ -778,7 +823,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// <returns>The converted value.</returns>
     public static explicit operator bool?(OpenIddictParameter? parameter)
     {
-        return parameter?.Value switch
+        return parameter?._value switch
         {
             // When the parameter is a null value or a JsonElement representing null, return null.
             null or JsonElement { ValueKind: JsonValueKind.Null or JsonValueKind.Undefined } => null,
@@ -833,7 +878,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// <returns>The converted value.</returns>
     public static explicit operator JsonElement(OpenIddictParameter? parameter)
     {
-        return parameter?.Value switch
+        return parameter?._value switch
         {
             // When the parameter is a null value, return an undefined JsonElement.
             null => default,
@@ -876,13 +921,14 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// <returns>The converted value.</returns>
     public static explicit operator JsonNode?(OpenIddictParameter? parameter)
     {
-        return parameter?.Value switch
+        return parameter?._value switch
         {
             // When the parameter is a null value or a JsonElement representing null, return null.
             null or JsonElement { ValueKind: JsonValueKind.Null or JsonValueKind.Undefined } => null,
 
-            // When the parameter is already a JsonNode, return it as-is.
-            JsonNode value => value,
+            // When the parameter is already a JsonNode, return a clone to ensure mutations
+            // made on the returned object do not affect the instance stored by this structure.
+            JsonNode value => value.DeepClone(),
 
             // When the parameter is a boolean, return a JsonValue.
             bool value => JsonValue.Create(value),
@@ -972,7 +1018,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// <returns>The converted value.</returns>
     public static explicit operator long?(OpenIddictParameter? parameter)
     {
-        return parameter?.Value switch
+        return parameter?._value switch
         {
             // When the parameter is a null value or a JsonElement representing null, return null.
             null or JsonElement { ValueKind: JsonValueKind.Null or JsonValueKind.Undefined } => null,
@@ -1030,7 +1076,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// <returns>The converted value.</returns>
     public static explicit operator string?(OpenIddictParameter? parameter)
     {
-        return parameter?.Value switch
+        return parameter?._value switch
         {
             // When the parameter is a null value or a JsonElement representing null, return null.
             null or JsonElement { ValueKind: JsonValueKind.Null or JsonValueKind.Undefined } => null,
@@ -1091,19 +1137,145 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     }
 
     /// <summary>
-    /// Converts an <see cref="OpenIddictParameter"/> instance to an array of strings.
+    /// Converts an <see cref="OpenIddictParameter"/> instance to a <see cref="StringValues"/> instance.
     /// </summary>
     /// <param name="parameter">The parameter to convert.</param>
     /// <returns>The converted value.</returns>
-    public static explicit operator string?[]?(OpenIddictParameter? parameter)
+    public static explicit operator StringValues(OpenIddictParameter? parameter)
+        => ((StringValues?) parameter).GetValueOrDefault();
+
+    /// <summary>
+    /// Converts an <see cref="OpenIddictParameter"/> instance to a <see cref="StringValues"/> instance.
+    /// </summary>
+    /// <param name="parameter">The parameter to convert.</param>
+    /// <returns>The converted value.</returns>
+    public static explicit operator StringValues?(OpenIddictParameter? parameter)
     {
-        return parameter?.Value switch
+        return parameter?._value switch
+        {
+            // When the parameter is a null value or a JsonElement representing null, return null.
+            null or JsonElement { ValueKind: JsonValueKind.Null or JsonValueKind.Undefined } => null,
+
+            // When the parameter is an array of strings, return a StringValues instance wrapping the cloned array.
+            string?[] value => new StringValues(value.ToArray().ToArray()),
+
+            // When the parameter is a string value, return a StringValues instance with a single entry.
+            string value => new StringValues(value),
+
+            // When the parameter is a boolean value, return a StringValues instance with its string representation.
+            bool value => new StringValues(value ? "true" : "false"),
+
+            // When the parameter is an integer, return a StringValues instance with its string representation.
+            long value => new StringValues(value.ToString(CultureInfo.InvariantCulture)),
+
+            // When the parameter is a JSON boolean value, return a StringValues instance with its string representation.
+            JsonElement { ValueKind: JsonValueKind.True  } => new StringValues("true"),
+            JsonElement { ValueKind: JsonValueKind.False } => new StringValues("false"),
+
+            // When the parameter is a JsonElement, try to convert it if it's of a supported type.
+            JsonElement value => ConvertFromJsonElement(value),
+
+            // When the parameter is a JsonValue wrapping a JsonElement,
+            // apply the same logic as with direct JsonElement instances.
+            JsonValue value when value.TryGetValue(out JsonElement element) => ConvertFromJsonElement(element),
+
+            // When the parameter is a JsonValue wrapping a string, return a StringValues instance with a single entry.
+            JsonValue value when value.TryGetValue(out string? result) => new StringValues(result),
+
+            // When the parameter is a JsonValue wrapping a boolean, return a StringValues instance with its string representation.
+            JsonValue value when value.TryGetValue(out bool result)
+                => new StringValues(result ? "true" : "false"),
+
+            // When the parameter is a JsonValue wrapping an integer, return a StringValues instance with its string representation.
+            JsonValue value when value.TryGetValue(out int result)
+                => new StringValues(result.ToString(CultureInfo.InvariantCulture)),
+
+            JsonValue value when value.TryGetValue(out long result)
+                => new StringValues(result.ToString(CultureInfo.InvariantCulture)),
+
+            // When the parameter is a JsonNode (e.g a JsonValue wrapping a non-primitive type),
+            // serialize it to a JsonElement first to determine its actual JSON representation
+            // and apply the same logic as with non-wrapped JsonElement instances.
+            JsonNode value when JsonSerializer.SerializeToElement(value) is JsonElement element
+                => ConvertFromJsonElement(element),
+
+            // If the parameter is of a different type, return null to indicate the conversion failed.
+            _ => null
+        };
+
+        static StringValues? ConvertFromJsonElement(JsonElement element) => element.ValueKind switch
+        {
+            // When the parameter is a JsonElement representing a boolean,
+            // return a StringValues instance with its string representation.
+            JsonValueKind.True  => new StringValues("true"),
+            JsonValueKind.False => new StringValues("false"),
+
+            // When the parameter is a JsonElement representing a string or a
+            // number, return a StringValues instance with its string representation.
+            JsonValueKind.String or JsonValueKind.Number => new StringValues(element.ToString()),
+
+            // When the parameter is a JsonElement representing an array, return the elements as strings.
+            JsonValueKind.Array => CreateArrayFromJsonElement(element),
+
+            _ => null
+        };
+
+        static StringValues? CreateArrayFromJsonElement(JsonElement element)
+        {
+            var length = element.GetArrayLength();
+            var array = new string[length];
+
+            for (var index = 0; index < length; index++)
+            {
+                var item = element[index];
+                if (item.ValueKind is JsonValueKind.True)
+                {
+                    array[index] = "true";
+                }
+
+                else if (item.ValueKind is JsonValueKind.False)
+                {
+                    array[index] = "false";
+                }
+
+                else if (item.ValueKind is JsonValueKind.String or JsonValueKind.Number)
+                {
+                    array[index] = item.ToString();
+                }
+
+                // Always return a null array if one of the items is a not string, a number or a boolean.
+                else
+                {
+                    return null;
+                }
+            }
+
+            return new StringValues(array);
+        }
+    }
+
+    /// <summary>
+    /// Converts an <see cref="OpenIddictParameter"/> instance to an immutable array of strings.
+    /// </summary>
+    /// <param name="parameter">The parameter to convert.</param>
+    /// <returns>The converted value.</returns>
+    public static explicit operator ImmutableArray<string?>(OpenIddictParameter? parameter)
+        => ((ImmutableArray<string?>?) parameter).GetValueOrDefault();
+
+    /// <summary>
+    /// Converts an <see cref="OpenIddictParameter"/> instance to an immutable array of strings.
+    /// </summary>
+    /// <param name="parameter">The parameter to convert.</param>
+    /// <returns>The converted value.</returns>
+    public static explicit operator ImmutableArray<string?>?(OpenIddictParameter? parameter)
+    {
+        return parameter?._value switch
         {
             // When the parameter is a null value or a JsonElement representing null, return null.
             null or JsonElement { ValueKind: JsonValueKind.Null or JsonValueKind.Undefined } => null,
 
             // When the parameter is already an array of strings, return it as-is.
-            string?[] value => value,
+            string?[] value => ImmutableCollectionsMarshal.AsImmutableArray(value),
 
             // When the parameter is a string value, return an array with a single entry.
             string value => [value],
@@ -1149,7 +1321,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
             _ => null
         };
 
-        static string?[]? ConvertFromJsonElement(JsonElement element) => element.ValueKind switch
+        static ImmutableArray<string?>? ConvertFromJsonElement(JsonElement element) => element.ValueKind switch
         {
             // When the parameter is a JsonElement representing a boolean,
             // return an 1-item array with its string representation.
@@ -1166,27 +1338,27 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
             _ => null
         };
 
-        static string?[]? CreateArrayFromJsonElement(JsonElement element)
+        static ImmutableArray<string?>? CreateArrayFromJsonElement(JsonElement element)
         {
             var length = element.GetArrayLength();
-            var array = new string?[length];
+            var builder = ImmutableArray.CreateBuilder<string?>(length);
 
             for (var index = 0; index < length; index++)
             {
                 var item = element[index];
                 if (item.ValueKind is JsonValueKind.True)
                 {
-                    array[index] = "true";
+                    builder.Add("true");
                 }
 
                 else if (item.ValueKind is JsonValueKind.False)
                 {
-                    array[index] = "false";
+                    builder.Add("false");
                 }
 
                 else if (item.ValueKind is JsonValueKind.String or JsonValueKind.Number)
                 {
-                    array[index] = item.ToString();
+                    builder.Add(item.ToString());
                 }
 
                 // Always return a null array if one of the items is a not string, a number or a boolean.
@@ -1196,65 +1368,96 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
                 }
             }
 
-            return array;
+            return builder.ToImmutable();
         }
     }
 
     /// <summary>
     /// Converts a boolean to an <see cref="OpenIddictParameter"/> instance.
     /// </summary>
-    /// <param name="value">The value to convert</param>
+    /// <param name="value">The value to convert.</param>
     /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
     public static implicit operator OpenIddictParameter(bool value) => new(value);
 
     /// <summary>
     /// Converts a nullable boolean to an <see cref="OpenIddictParameter"/> instance.
     /// </summary>
-    /// <param name="value">The value to convert</param>
+    /// <param name="value">The value to convert.</param>
     /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
     public static implicit operator OpenIddictParameter(bool? value) => new(value);
 
     /// <summary>
     /// Converts a <see cref="JsonElement"/> to an <see cref="OpenIddictParameter"/> instance.
     /// </summary>
-    /// <param name="value">The value to convert</param>
+    /// <param name="value">The value to convert.</param>
     /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
     public static implicit operator OpenIddictParameter(JsonElement value) => new(value);
 
     /// <summary>
     /// Converts a <see cref="JsonNode"/> to an <see cref="OpenIddictParameter"/> instance.
     /// </summary>
-    /// <param name="value">The value to convert</param>
+    /// <param name="value">The value to convert.</param>
     /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
     public static implicit operator OpenIddictParameter(JsonNode? value) => new(value);
 
     /// <summary>
     /// Converts a long integer to an <see cref="OpenIddictParameter"/> instance.
     /// </summary>
-    /// <param name="value">The value to convert</param>
+    /// <param name="value">The value to convert.</param>
     /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
     public static implicit operator OpenIddictParameter(long value) => new(value);
 
     /// <summary>
     /// Converts a nullable long integer to an <see cref="OpenIddictParameter"/> instance.
     /// </summary>
-    /// <param name="value">The value to convert</param>
+    /// <param name="value">The value to convert.</param>
     /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
     public static implicit operator OpenIddictParameter(long? value) => new(value);
 
     /// <summary>
     /// Converts a string to an <see cref="OpenIddictParameter"/> instance.
     /// </summary>
-    /// <param name="value">The value to convert</param>
+    /// <param name="value">The value to convert.</param>
     /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
     public static implicit operator OpenIddictParameter(string? value) => new(value);
 
+    /// <summary>
+    /// Converts a string to an <see cref="OpenIddictParameter"/> instance.
+    /// </summary>
+    /// <param name="value">The value to convert.</param>
+    /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
+    public static implicit operator OpenIddictParameter(StringValues? value) => value?.Count switch
+    {
+        null or 0 => default,
+        1         => new OpenIddictParameter(value.GetValueOrDefault()[0]),
+        _         => new(ImmutableCollectionsMarshal.AsImmutableArray(value.GetValueOrDefault().ToArray()))
+    };
+
+    /// <summary>
+    /// Converts a string to an <see cref="OpenIddictParameter"/> instance.
+    /// </summary>
+    /// <param name="value">The value to convert.</param>
+    /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
+    public static implicit operator OpenIddictParameter(StringValues value) => value.Count switch
+    {
+        0 => default,
+        1 => new OpenIddictParameter(value[0]),
+        _ => new(ImmutableCollectionsMarshal.AsImmutableArray(value.ToArray()))
+    };
+
+    /// <summary>
+    /// Converts an array of strings to an <see cref="OpenIddictParameter"/> instance.
+    /// </summary>
+    /// <param name="value">The value to convert.</param>
+    /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
+    public static implicit operator OpenIddictParameter(ImmutableArray<string?> value) => new(value);
+
     /// <summary>
     /// Converts an array of strings to an <see cref="OpenIddictParameter"/> instance.
     /// </summary>
-    /// <param name="value">The value to convert</param>
+    /// <param name="value">The value to convert.</param>
     /// <returns>An <see cref="OpenIddictParameter"/> instance.</returns>
-    public static implicit operator OpenIddictParameter(string?[]? value) => new(value);
+    public static implicit operator OpenIddictParameter(ImmutableArray<string?>? value) => new(value);
 
     /// <summary>
     /// Determines whether a parameter is null or empty.
@@ -1263,7 +1466,7 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
     /// <returns><see langword="true"/> if the parameter is null or empty, <see langword="false"/> otherwise.</returns>
     public static bool IsNullOrEmpty(OpenIddictParameter parameter)
     {
-        return parameter.Value switch
+        return parameter._value switch
         {
             null or JsonElement { ValueKind: JsonValueKind.Null or JsonValueKind.Undefined } => true,
 
@@ -1298,11 +1501,14 @@ public readonly struct OpenIddictParameter : IEquatable<OpenIddictParameter>
                     return element.GetArrayLength() is 0;
 
                 case JsonValueKind.Object:
+#if SUPPORTS_JSON_ELEMENT_PROPERTY_COUNT
+                    return element.GetPropertyCount() is 0;
+#else
                     using (var enumerator = element.EnumerateObject())
                     {
                         return !enumerator.MoveNext();
                     }
-
+#endif
                 default: return false;
             }
         }

src/OpenIddict.Abstractions/Primitives/OpenIddictRequest.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Collections.Specialized;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
@@ -79,7 +80,7 @@ public class OpenIddictRequest : OpenIddictMessage
     /// </summary>
     /// <param name="parameters">The request parameters.</param>
     /// <remarks>Parameters with a null or empty key are always ignored.</remarks>
-    public OpenIddictRequest(IEnumerable<KeyValuePair<string, string?[]?>> parameters)
+    public OpenIddictRequest(IEnumerable<KeyValuePair<string, ImmutableArray<string?>?>> parameters)
         : base(parameters)
     {
     }
@@ -134,18 +135,18 @@ public class OpenIddictRequest : OpenIddictMessage
     /// <summary>
     /// Gets or sets the "audience" parameters.
     /// </summary>
-    public string?[]? Audiences
+    public ImmutableArray<string?>? Audiences
     {
-        get => (string?[]?) GetParameter(OpenIddictConstants.Parameters.Audience);
+        get => (ImmutableArray<string?>?) GetParameter(OpenIddictConstants.Parameters.Audience);
         set => SetParameter(OpenIddictConstants.Parameters.Audience, value);
     }
 
     /// <summary>
     /// Gets or sets the "claims" parameter.
     /// </summary>
-    public JsonElement Claims
+    public JsonObject? Claims
     {
-        get => (JsonElement) GetParameter(OpenIddictConstants.Parameters.Claims);
+        get => (JsonObject?) GetParameter(OpenIddictConstants.Parameters.Claims);
         set => SetParameter(OpenIddictConstants.Parameters.Claims, value);
     }
 
@@ -379,9 +380,9 @@ public class OpenIddictRequest : OpenIddictMessage
     /// <summary>
     /// Gets or sets the "resource" parameters.
     /// </summary>
-    public string?[]? Resources
+    public ImmutableArray<string?>? Resources
     {
-        get => (string?[]?) GetParameter(OpenIddictConstants.Parameters.Resource);
+        get => (ImmutableArray<string?>?) GetParameter(OpenIddictConstants.Parameters.Resource);
         set => SetParameter(OpenIddictConstants.Parameters.Resource, value);
     }
 
@@ -442,9 +443,9 @@ public class OpenIddictRequest : OpenIddictMessage
     /// <summary>
     /// Gets or sets the "registration" parameter.
     /// </summary>
-    public JsonElement Registration
+    public JsonObject? Registration
     {
-        get => (JsonElement) GetParameter(OpenIddictConstants.Parameters.Registration);
+        get => (JsonObject?) GetParameter(OpenIddictConstants.Parameters.Registration);
         set => SetParameter(OpenIddictConstants.Parameters.Registration, value);
     }
 

src/OpenIddict.Abstractions/Primitives/OpenIddictResponse.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Collections.Specialized;
 using System.Diagnostics;
 using System.Text.Json;
@@ -78,7 +79,7 @@ public class OpenIddictResponse : OpenIddictMessage
     /// </summary>
     /// <param name="parameters">The response parameters.</param>
     /// <remarks>Parameters with a null or empty key are always ignored.</remarks>
-    public OpenIddictResponse(IEnumerable<KeyValuePair<string, string?[]?>> parameters)
+    public OpenIddictResponse(IEnumerable<KeyValuePair<string, ImmutableArray<string?>?>> parameters)
         : base(parameters)
     {
     }

src/OpenIddict.Client.AspNetCore/OpenIddictClientAspNetCoreHandlers.Authentication.cs

@@ -78,9 +78,9 @@ public static partial class OpenIddictClientAspNetCoreHandlers
 #if SUPPORTS_MULTIPLE_VALUES_IN_QUERYHELPERS
                 var location = QueryHelpers.AddQueryString(context.AuthorizationEndpoint,
                     from parameter in context.Request.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select KeyValuePair.Create(parameter.Key, value));
 #else
@@ -88,9 +88,9 @@ public static partial class OpenIddictClientAspNetCoreHandlers
 
                 foreach (var (key, value) in
                     from parameter in context.Request.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {

src/OpenIddict.Client.AspNetCore/OpenIddictClientAspNetCoreHandlers.Session.cs

@@ -78,9 +78,9 @@ public static partial class OpenIddictClientAspNetCoreHandlers
 #if SUPPORTS_MULTIPLE_VALUES_IN_QUERYHELPERS
                 var location = QueryHelpers.AddQueryString(context.EndSessionEndpoint,
                     from parameter in context.Request.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select KeyValuePair.Create(parameter.Key, value));
 #else
@@ -88,9 +88,9 @@ public static partial class OpenIddictClientAspNetCoreHandlers
 
                 foreach (var (key, value) in
                     from parameter in context.Request.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {

src/OpenIddict.Client.AspNetCore/OpenIddictClientAspNetCoreHandlers.cs

@@ -8,6 +8,7 @@ using System.Buffers.Binary;
 using System.Collections.Immutable;
 using System.ComponentModel;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 using System.Security.Claims;
 using System.Text;
 using System.Text.Json;
@@ -622,13 +623,17 @@ public static partial class OpenIddictClientAspNetCoreHandlers
                     context.Parameters[parameter.Key] = parameter.Value switch
                     {
                         OpenIddictParameter value => value,
-                        JsonElement         value => new OpenIddictParameter(value),
-                        JsonNode            value => new OpenIddictParameter(value),
-                        bool                value => new OpenIddictParameter(value),
-                        int                 value => new OpenIddictParameter(value),
-                        long                value => new OpenIddictParameter(value),
-                        string              value => new OpenIddictParameter(value),
-                        string[]            value => new OpenIddictParameter(value),
+
+                        JsonElement             value => new OpenIddictParameter(value),
+                        JsonNode                value => new OpenIddictParameter(value),
+                        bool                    value => new OpenIddictParameter(value),
+                        int                     value => new OpenIddictParameter(value),
+                        long                    value => new OpenIddictParameter(value),
+                        string                  value => new OpenIddictParameter(value),
+                        ImmutableArray<string?> value => new OpenIddictParameter(value),
+
+                        string?[]            value => new(ImmutableCollectionsMarshal.AsImmutableArray(value)),
+                        IEnumerable<string?> value => new OpenIddictParameter([.. value]),
 
                         _ => throw new InvalidOperationException(SR.GetResourceString(SR.ID0115))
                     };
@@ -943,13 +948,17 @@ public static partial class OpenIddictClientAspNetCoreHandlers
                     context.Parameters[parameter.Key] = parameter.Value switch
                     {
                         OpenIddictParameter value => value,
-                        JsonElement         value => new OpenIddictParameter(value),
-                        JsonNode            value => new OpenIddictParameter(value),
-                        bool                value => new OpenIddictParameter(value),
-                        int                 value => new OpenIddictParameter(value),
-                        long                value => new OpenIddictParameter(value),
-                        string              value => new OpenIddictParameter(value),
-                        string[]            value => new OpenIddictParameter(value),
+
+                        JsonElement             value => new OpenIddictParameter(value),
+                        JsonNode                value => new OpenIddictParameter(value),
+                        bool                    value => new OpenIddictParameter(value),
+                        int                     value => new OpenIddictParameter(value),
+                        long                    value => new OpenIddictParameter(value),
+                        string                  value => new OpenIddictParameter(value),
+                        ImmutableArray<string?> value => new OpenIddictParameter(value),
+
+                        string?[]            value => new(ImmutableCollectionsMarshal.AsImmutableArray(value)),
+                        IEnumerable<string?> value => new OpenIddictParameter([.. value]),
 
                         _ => throw new InvalidOperationException(SR.GetResourceString(SR.ID0115))
                     };

src/OpenIddict.Client.DataProtection/OpenIddictClientDataProtectionFormatter.cs

@@ -52,7 +52,7 @@ public sealed class OpenIddictClientDataProtectionFormatter : IOpenIddictClientD
         {
             // Read the version of the format used to serialize the ticket.
             var version = reader.ReadInt32();
-            if (version != 5)
+            if (version is not 5)
             {
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0287));
             }

src/OpenIddict.Client.Owin/OpenIddictClientOwinHandlers.Authentication.cs

@@ -78,9 +78,9 @@ public static partial class OpenIddictClientOwinHandlers
                 // For consistency, multiple parameters with the same name are also supported by this endpoint.
                 foreach (var (key, value) in
                     from parameter in context.Request.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {

src/OpenIddict.Client.Owin/OpenIddictClientOwinHandlers.Session.cs

@@ -76,9 +76,9 @@ public static partial class OpenIddictClientOwinHandlers
                 // For consistency, multiple parameters with the same name are also supported by this endpoint.
                 foreach (var (key, value) in
                     from parameter in context.Request.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {

src/OpenIddict.Client.Owin/OpenIddictClientOwinHandlers.cs

@@ -14,6 +14,7 @@ using System.Text;
 using System.Text.Json;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
+using Microsoft.Extensions.Primitives;
 using Microsoft.IdentityModel.Tokens;
 using OpenIddict.Extensions;
 using Owin;
@@ -265,7 +266,10 @@ public static partial class OpenIddictClientOwinHandlers
 
             if (string.Equals(request.Method, "GET", StringComparison.OrdinalIgnoreCase))
             {
-                context.Transaction.Request = new OpenIddictRequest(request.Query);
+                context.Transaction.Request = new OpenIddictRequest(
+                    from parameter in request.Query
+                    let values = new StringValues(parameter.Value)
+                    select new KeyValuePair<string, StringValues>(parameter.Key, values));
             }
 
             else if (string.Equals(request.Method, "POST", StringComparison.OrdinalIgnoreCase))
@@ -296,7 +300,10 @@ public static partial class OpenIddictClientOwinHandlers
                     return;
                 }
 
-                context.Transaction.Request = new OpenIddictRequest(await request.ReadFormAsync());
+                context.Transaction.Request = new OpenIddictRequest(
+                    from parameter in await request.ReadFormAsync()
+                    let values = new StringValues(parameter.Value)
+                    select new KeyValuePair<string, StringValues>(parameter.Key, values));
             }
 
             else

src/OpenIddict.Client.SystemIntegration/OpenIddictClientSystemIntegrationActivationHandler.cs

@@ -6,6 +6,7 @@
 
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Options;
 
@@ -78,7 +79,9 @@ public sealed class OpenIddictClientSystemIntegrationActivationHandler : IHosted
             }
 #endif
             // Otherwise, try to extract the protocol activation from the command line arguments.
-            if (GetProtocolActivationUriFromCommandLineArguments(Environment.GetCommandLineArgs()) is Uri value)
+            var arguments = ImmutableCollectionsMarshal.AsImmutableArray(Environment.GetCommandLineArgs());
+
+            if (GetProtocolActivationUriFromCommandLineArguments(arguments) is Uri value)
             {
                 return new OpenIddictClientSystemIntegrationActivation(value);
             }

src/OpenIddict.Client.SystemIntegration/OpenIddictClientSystemIntegrationHandlers.Authentication.cs

@@ -240,8 +240,8 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                     NSUrl CreateUrl() => new(OpenIddictHelpers.AddQueryStringParameters(
                         uri: new Uri(context.AuthorizationEndpoint, UriKind.Absolute),
                         parameters: context.Transaction.Request.GetParameters().ToDictionary(
-                            parameter => parameter.Key,
-                            parameter => new StringValues((string?[]?) parameter.Value))).AbsoluteUri);
+                            static parameter => parameter.Key,
+                            static parameter => (StringValues) parameter.Value)).AbsoluteUri);
 
                     void HandleCallback(NSUrl? url, NSError? error)
                     {
@@ -253,12 +253,7 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                             {
                                 foreach (var parameter in OpenIddictHelpers.ParseQuery(url.Query))
                                 {
-                                    parameters[parameter.Key] = parameter.Value.Count switch
-                                    {
-                                        0 => default,
-                                        1 => parameter.Value[0],
-                                        _ => parameter.Value.ToArray()
-                                    };
+                                    parameters[parameter.Key] = parameter.Value;
                                 }
                             }
 
@@ -270,12 +265,7 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                             {
                                 foreach (var parameter in OpenIddictHelpers.ParseFragment(url.Fragment))
                                 {
-                                    parameters[parameter.Key] = parameter.Value.Count switch
-                                    {
-                                        0 => default,
-                                        1 => parameter.Value[0],
-                                        _ => parameter.Value.ToArray()
-                                    };
+                                    parameters[parameter.Key] = parameter.Value;
                                 }
                             }
 
@@ -370,8 +360,8 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                 intent.LaunchUrl(Application.Context, NativeUri.Parse(OpenIddictHelpers.AddQueryStringParameters(
                     uri: new Uri(context.AuthorizationEndpoint, UriKind.Absolute),
                     parameters: context.Transaction.Request.GetParameters().ToDictionary(
-                        parameter => parameter.Key,
-                        parameter => new StringValues((string?[]?) parameter.Value))).AbsoluteUri)!);
+                        static parameter => parameter.Key,
+                        static parameter => (StringValues) parameter.Value)).AbsoluteUri)!);
 
                 context.HandleRequest();
 #else
@@ -455,8 +445,8 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                     requestUri : OpenIddictHelpers.AddQueryStringParameters(
                         uri: new Uri(context.AuthorizationEndpoint, UriKind.Absolute),
                         parameters: context.Transaction.Request.GetParameters().ToDictionary(
-                            parameter => parameter.Key,
-                            parameter => new StringValues((string?[]?) parameter.Value))),
+                            static parameter => parameter.Key,
+                            static parameter => (StringValues) parameter.Value)),
                     callbackUri: new Uri(context.RedirectUri, UriKind.Absolute)))
                 {
                     case { ResponseStatus: WebAuthenticationStatus.Success } result
@@ -467,12 +457,7 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                         {
                             foreach (var parameter in OpenIddictHelpers.ParseQuery(uri.Query))
                             {
-                                parameters[parameter.Key] = parameter.Value.Count switch
-                                {
-                                    0 => default,
-                                    1 => parameter.Value[0],
-                                    _ => parameter.Value.ToArray()
-                                };
+                                parameters[parameter.Key] = parameter.Value;
                             }
                         }
 
@@ -484,12 +469,7 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                         {
                             foreach (var parameter in OpenIddictHelpers.ParseFragment(uri.Fragment))
                             {
-                                parameters[parameter.Key] = parameter.Value.Count switch
-                                {
-                                    0 => default,
-                                    1 => parameter.Value[0],
-                                    _ => parameter.Value.ToArray()
-                                };
+                                parameters[parameter.Key] = parameter.Value;
                             }
                         }
 
@@ -576,8 +556,8 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                 var uri = OpenIddictHelpers.AddQueryStringParameters(
                     uri: new Uri(context.AuthorizationEndpoint, UriKind.Absolute),
                     parameters: context.Transaction.Request.GetParameters().ToDictionary(
-                        parameter => parameter.Key,
-                        parameter => new StringValues((string?[]?) parameter.Value)));
+                        static parameter => parameter.Key,
+                        static parameter => (StringValues) parameter.Value));
 
                 if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
                 {

src/OpenIddict.Client.SystemIntegration/OpenIddictClientSystemIntegrationHandlers.Session.cs

@@ -240,8 +240,8 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                     NSUrl CreateUrl() => new(OpenIddictHelpers.AddQueryStringParameters(
                         uri: new Uri(context.EndSessionEndpoint, UriKind.Absolute),
                         parameters: context.Transaction.Request.GetParameters().ToDictionary(
-                            parameter => parameter.Key,
-                            parameter => new StringValues((string?[]?) parameter.Value))).AbsoluteUri);
+                            static parameter => parameter.Key,
+                            static parameter => (StringValues) parameter.Value)).AbsoluteUri);
 
                     void HandleCallback(NSUrl? url, NSError? error)
                     {
@@ -253,12 +253,7 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                             {
                                 foreach (var parameter in OpenIddictHelpers.ParseQuery(url.Query))
                                 {
-                                    parameters[parameter.Key] = parameter.Value.Count switch
-                                    {
-                                        0 => default,
-                                        1 => parameter.Value[0],
-                                        _ => parameter.Value.ToArray()
-                                    };
+                                    parameters[parameter.Key] = parameter.Value;
                                 }
                             }
 
@@ -270,12 +265,7 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                             {
                                 foreach (var parameter in OpenIddictHelpers.ParseFragment(url.Fragment))
                                 {
-                                    parameters[parameter.Key] = parameter.Value.Count switch
-                                    {
-                                        0 => default,
-                                        1 => parameter.Value[0],
-                                        _ => parameter.Value.ToArray()
-                                    };
+                                    parameters[parameter.Key] = parameter.Value;
                                 }
                             }
 
@@ -370,8 +360,8 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                 intent.LaunchUrl(Application.Context, NativeUri.Parse(OpenIddictHelpers.AddQueryStringParameters(
                     uri: new Uri(context.EndSessionEndpoint, UriKind.Absolute),
                     parameters: context.Transaction.Request.GetParameters().ToDictionary(
-                        parameter => parameter.Key,
-                        parameter => new StringValues((string?[]?) parameter.Value))).AbsoluteUri)!);
+                        static parameter => parameter.Key,
+                        static parameter => (StringValues) parameter.Value)).AbsoluteUri)!);
 
                 context.HandleRequest();
 #else
@@ -455,8 +445,8 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                     requestUri : OpenIddictHelpers.AddQueryStringParameters(
                         uri: new Uri(context.EndSessionEndpoint, UriKind.Absolute),
                         parameters: context.Transaction.Request.GetParameters().ToDictionary(
-                            parameter => parameter.Key,
-                            parameter => new StringValues((string?[]?) parameter.Value))),
+                            static parameter => parameter.Key,
+                            static parameter => (StringValues) parameter.Value)),
                     callbackUri: new Uri(context.PostLogoutRedirectUri, UriKind.Absolute)))
                 {
                     case { ResponseStatus: WebAuthenticationStatus.Success } result
@@ -467,12 +457,7 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                         {
                             foreach (var parameter in OpenIddictHelpers.ParseQuery(uri.Query))
                             {
-                                parameters[parameter.Key] = parameter.Value.Count switch
-                                {
-                                    0 => default,
-                                    1 => parameter.Value[0],
-                                    _ => parameter.Value.ToArray()
-                                };
+                                parameters[parameter.Key] = parameter.Value;
                             }
                         }
 
@@ -484,12 +469,7 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                         {
                             foreach (var parameter in OpenIddictHelpers.ParseFragment(uri.Fragment))
                             {
-                                parameters[parameter.Key] = parameter.Value.Count switch
-                                {
-                                    0 => default,
-                                    1 => parameter.Value[0],
-                                    _ => parameter.Value.ToArray()
-                                };
+                                parameters[parameter.Key] = parameter.Value;
                             }
                         }
 
@@ -576,8 +556,8 @@ public static partial class OpenIddictClientSystemIntegrationHandlers
                 var uri = OpenIddictHelpers.AddQueryStringParameters(
                     uri: new Uri(context.EndSessionEndpoint, UriKind.Absolute),
                     parameters: context.Transaction.Request.GetParameters().ToDictionary(
-                        parameter => parameter.Key,
-                        parameter => new StringValues((string?[]?) parameter.Value)));
+                        static parameter => parameter.Key,
+                        static parameter => (StringValues) parameter.Value));
 
                 if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
                 {

src/OpenIddict.Client.SystemIntegration/OpenIddictClientSystemIntegrationHelpers.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.ComponentModel;
 using System.Diagnostics;
 using System.Net;
@@ -378,7 +379,7 @@ public static class OpenIddictClientSystemIntegrationHelpers
     /// The <see cref="Uri"/> if the application instance was activated
     /// via a protocol activation, <see langword="null"/> otherwise.
     /// </returns>
-    internal static Uri? GetProtocolActivationUriFromCommandLineArguments(string?[]? arguments) => arguments switch
+    internal static Uri? GetProtocolActivationUriFromCommandLineArguments(ImmutableArray<string> arguments) => arguments switch
     {
         // In most cases, the first segment present in the command line arguments contains the path of the
         // executable, but it's technically possible to start an application in a way that the command line

src/OpenIddict.Client.SystemIntegration/OpenIddictClientSystemIntegrationService.cs

@@ -69,12 +69,7 @@ public sealed class OpenIddictClientSystemIntegrationService
         {
             foreach (var parameter in OpenIddictHelpers.ParseQuery(intent.Data.Query))
             {
-                parameters[parameter.Key] = parameter.Value.Count switch
-                {
-                    0 => default,
-                    1 => parameter.Value[0],
-                    _ => parameter.Value.ToArray()
-                };
+                parameters[parameter.Key] = parameter.Value;
             }
         }
 
@@ -86,12 +81,7 @@ public sealed class OpenIddictClientSystemIntegrationService
         {
             foreach (var parameter in OpenIddictHelpers.ParseFragment(intent.Data.Fragment))
             {
-                parameters[parameter.Key] = parameter.Value.Count switch
-                {
-                    0 => default,
-                    1 => parameter.Value[0],
-                    _ => parameter.Value.ToArray()
-                };
+                parameters[parameter.Key] = parameter.Value;
             }
         }
 

src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpHandlers.cs

@@ -1044,8 +1044,8 @@ public static partial class OpenIddictClientSystemNetHttpHandlers
             {
                 request.RequestUri = OpenIddictHelpers.AddQueryStringParameters(request.RequestUri,
                     context.Transaction.Request.GetParameters().ToDictionary(
-                        parameter => parameter.Key,
-                        parameter => new StringValues((string?[]?) parameter.Value)));
+                        static parameter => parameter.Key,
+                        static parameter => (StringValues) parameter.Value));
             }
 
             // For POST requests, attach the request parameters to the request form by default.
@@ -1053,9 +1053,9 @@ public static partial class OpenIddictClientSystemNetHttpHandlers
             {
                 request.Content = new FormUrlEncodedContent(
                     from parameter in context.Transaction.Request.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     select new KeyValuePair<string?, string?>(parameter.Key, value));
             }
 

src/OpenIddict.Client/OpenIddictClientHandlers.Discovery.cs

@@ -1486,24 +1486,12 @@ public static partial class OpenIddictClientHandlers
 
                     // The following parameters MUST be formatted as arrays of objects:
                     JsonWebKeySetParameterNames.Keys => ((JsonElement) value) is JsonElement element &&
-                        element.ValueKind is JsonValueKind.Array && ValidateObjectArray(element),
+                        element.ValueKind is JsonValueKind.Array &&
+                        OpenIddictHelpers.ValidateArrayElements(element, JsonValueKind.Object),
 
                     // Parameters that are not in the well-known list can be of any type.
                     _ => true
                 };
-
-                static bool ValidateObjectArray(JsonElement element)
-                {
-                    foreach (var item in element.EnumerateArray())
-                    {
-                        if (item.ValueKind is not JsonValueKind.Object)
-                        {
-                            return false;
-                        }
-                    }
-
-                    return true;
-                }
             }
         }
 

src/OpenIddict.Server.AspNetCore/OpenIddictServerAspNetCoreHandlers.Authentication.cs

@@ -102,9 +102,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
 #if SUPPORTS_MULTIPLE_VALUES_IN_QUERYHELPERS
                 var location = QueryHelpers.AddQueryString(context.RequestUri.GetLeftPart(UriPartial.Path),
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select KeyValuePair.Create(parameter.Key, value));
 #else
@@ -112,9 +112,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
 
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {
@@ -188,9 +188,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
                 // For consistency, multiple parameters with the same name are also supported by this endpoint.
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {
@@ -264,9 +264,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
 #if SUPPORTS_MULTIPLE_VALUES_IN_QUERYHELPERS
                 var location = QueryHelpers.AddQueryString(context.RedirectUri,
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select KeyValuePair.Create(parameter.Key, value));
 #else
@@ -274,9 +274,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
 
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {
@@ -335,9 +335,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
                 // For consistency, multiple parameters with the same name are also supported by this endpoint.
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {

src/OpenIddict.Server.AspNetCore/OpenIddictServerAspNetCoreHandlers.Session.cs

@@ -84,9 +84,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
 #if SUPPORTS_MULTIPLE_VALUES_IN_QUERYHELPERS
                 var location = QueryHelpers.AddQueryString(context.RequestUri.GetLeftPart(UriPartial.Path),
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select KeyValuePair.Create(parameter.Key, value));
 #else
@@ -94,9 +94,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
 
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {
@@ -154,9 +154,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
 #if SUPPORTS_MULTIPLE_VALUES_IN_QUERYHELPERS
                 var location = QueryHelpers.AddQueryString(context.PostLogoutRedirectUri,
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select KeyValuePair.Create(parameter.Key, value));
 #else
@@ -164,9 +164,9 @@ public static partial class OpenIddictServerAspNetCoreHandlers
 
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {

src/OpenIddict.Server.AspNetCore/OpenIddictServerAspNetCoreHandlers.cs

@@ -7,6 +7,7 @@
 using System.Collections.Immutable;
 using System.ComponentModel;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 using System.Text;
 using System.Text.Encodings.Web;
 using System.Text.Json;
@@ -257,13 +258,17 @@ public static partial class OpenIddictServerAspNetCoreHandlers
                     context.Parameters[parameter.Key] = parameter.Value switch
                     {
                         OpenIddictParameter value => value,
-                        JsonElement         value => new OpenIddictParameter(value),
-                        JsonNode            value => new OpenIddictParameter(value),
-                        bool                value => new OpenIddictParameter(value),
-                        int                 value => new OpenIddictParameter(value),
-                        long                value => new OpenIddictParameter(value),
-                        string              value => new OpenIddictParameter(value),
-                        string[]            value => new OpenIddictParameter(value),
+
+                        JsonElement             value => new OpenIddictParameter(value),
+                        JsonNode                value => new OpenIddictParameter(value),
+                        bool                    value => new OpenIddictParameter(value),
+                        int                     value => new OpenIddictParameter(value),
+                        long                    value => new OpenIddictParameter(value),
+                        string                  value => new OpenIddictParameter(value),
+                        ImmutableArray<string?> value => new OpenIddictParameter(value),
+
+                        string?[]            value => new(ImmutableCollectionsMarshal.AsImmutableArray(value)),
+                        IEnumerable<string?> value => new OpenIddictParameter([.. value]),
 
                         _ => throw new InvalidOperationException(SR.GetResourceString(SR.ID0115))
                     };
@@ -354,13 +359,17 @@ public static partial class OpenIddictServerAspNetCoreHandlers
                     context.Parameters[parameter.Key] = parameter.Value switch
                     {
                         OpenIddictParameter value => value,
-                        JsonElement         value => new OpenIddictParameter(value),
-                        JsonNode            value => new OpenIddictParameter(value),
-                        bool                value => new OpenIddictParameter(value),
-                        int                 value => new OpenIddictParameter(value),
-                        long                value => new OpenIddictParameter(value),
-                        string              value => new OpenIddictParameter(value),
-                        string[]            value => new OpenIddictParameter(value),
+
+                        JsonElement             value => new OpenIddictParameter(value),
+                        JsonNode                value => new OpenIddictParameter(value),
+                        bool                    value => new OpenIddictParameter(value),
+                        int                     value => new OpenIddictParameter(value),
+                        long                    value => new OpenIddictParameter(value),
+                        string                  value => new OpenIddictParameter(value),
+                        ImmutableArray<string?> value => new OpenIddictParameter(value),
+
+                        string?[]            value => new(ImmutableCollectionsMarshal.AsImmutableArray(value)),
+                        IEnumerable<string?> value => new OpenIddictParameter([.. value]),
 
                         _ => throw new InvalidOperationException(SR.GetResourceString(SR.ID0115))
                     };
@@ -413,13 +422,17 @@ public static partial class OpenIddictServerAspNetCoreHandlers
                     context.Parameters[parameter.Key] = parameter.Value switch
                     {
                         OpenIddictParameter value => value,
-                        JsonElement         value => new OpenIddictParameter(value),
-                        JsonNode            value => new OpenIddictParameter(value),
-                        bool                value => new OpenIddictParameter(value),
-                        int                 value => new OpenIddictParameter(value),
-                        long                value => new OpenIddictParameter(value),
-                        string              value => new OpenIddictParameter(value),
-                        string[]            value => new OpenIddictParameter(value),
+
+                        JsonElement             value => new OpenIddictParameter(value),
+                        JsonNode                value => new OpenIddictParameter(value),
+                        bool                    value => new OpenIddictParameter(value),
+                        int                     value => new OpenIddictParameter(value),
+                        long                    value => new OpenIddictParameter(value),
+                        string                  value => new OpenIddictParameter(value),
+                        ImmutableArray<string?> value => new OpenIddictParameter(value),
+
+                        string?[]            value => new(ImmutableCollectionsMarshal.AsImmutableArray(value)),
+                        IEnumerable<string?> value => new OpenIddictParameter([.. value]),
 
                         _ => throw new InvalidOperationException(SR.GetResourceString(SR.ID0115))
                     };

src/OpenIddict.Server.DataProtection/OpenIddictServerDataProtectionFormatter.cs

@@ -61,7 +61,7 @@ public sealed class OpenIddictServerDataProtectionFormatter : IOpenIddictServerD
         {
             // Read the version of the format used to serialize the ticket.
             var version = reader.ReadInt32();
-            if (version != 5)
+            if (version is not 5)
             {
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0287));
             }

src/OpenIddict.Server.Owin/OpenIddictServerOwinHandlers.Authentication.cs

@@ -104,9 +104,9 @@ public static partial class OpenIddictServerOwinHandlers
                 var location = context.RequestUri.GetLeftPart(UriPartial.Path);
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {
@@ -180,9 +180,9 @@ public static partial class OpenIddictServerOwinHandlers
                 // For consistency, multiple parameters with the same name are also supported by this endpoint.
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {
@@ -256,9 +256,9 @@ public static partial class OpenIddictServerOwinHandlers
                 // For consistency, multiple parameters with the same name are also supported by this endpoint.
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {
@@ -317,9 +317,9 @@ public static partial class OpenIddictServerOwinHandlers
                 // For consistency, multiple parameters with the same name are also supported by this endpoint.
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {

src/OpenIddict.Server.Owin/OpenIddictServerOwinHandlers.Session.cs

@@ -84,9 +84,9 @@ public static partial class OpenIddictServerOwinHandlers
                 var location = context.RequestUri.GetLeftPart(UriPartial.Path);
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {
@@ -143,9 +143,9 @@ public static partial class OpenIddictServerOwinHandlers
                 // For consistency, multiple parameters with the same name are also supported by this endpoint.
                 foreach (var (key, value) in
                     from parameter in context.Response.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     where !string.IsNullOrEmpty(value)
                     select (parameter.Key, Value: value))
                 {

src/OpenIddict.Server.Owin/OpenIddictServerOwinHandlers.cs

@@ -13,6 +13,7 @@ using System.Text.Encodings.Web;
 using System.Text.Json;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
+using Microsoft.Extensions.Primitives;
 using OpenIddict.Extensions;
 using Owin;
 using static OpenIddict.Server.Owin.OpenIddictServerOwinConstants;
@@ -524,7 +525,10 @@ public static partial class OpenIddictServerOwinHandlers
 
             if (string.Equals(request.Method, "GET", StringComparison.OrdinalIgnoreCase))
             {
-                context.Transaction.Request = new OpenIddictRequest(request.Query);
+                context.Transaction.Request = new OpenIddictRequest(
+                    from parameter in request.Query
+                    let values = new StringValues(parameter.Value)
+                    select new KeyValuePair<string, StringValues>(parameter.Key, values));
             }
 
             else
@@ -575,7 +579,10 @@ public static partial class OpenIddictServerOwinHandlers
 
             if (string.Equals(request.Method, "GET", StringComparison.OrdinalIgnoreCase))
             {
-                context.Transaction.Request = new OpenIddictRequest(request.Query);
+                context.Transaction.Request = new OpenIddictRequest(
+                    from parameter in request.Query
+                    let values = new StringValues(parameter.Value)
+                    select new KeyValuePair<string, StringValues>(parameter.Key, values));
             }
 
             else if (string.Equals(request.Method, "POST", StringComparison.OrdinalIgnoreCase))
@@ -606,7 +613,10 @@ public static partial class OpenIddictServerOwinHandlers
                     return;
                 }
 
-                context.Transaction.Request = new OpenIddictRequest(await request.ReadFormAsync());
+                context.Transaction.Request = new OpenIddictRequest(
+                    from parameter in await request.ReadFormAsync()
+                    let values = new StringValues(parameter.Value)
+                    select new KeyValuePair<string, StringValues>(parameter.Key, values));
             }
 
             else
@@ -681,7 +691,10 @@ public static partial class OpenIddictServerOwinHandlers
                     return;
                 }
 
-                context.Transaction.Request = new OpenIddictRequest(await request.ReadFormAsync());
+                context.Transaction.Request = new OpenIddictRequest(
+                    from parameter in await request.ReadFormAsync()
+                    let values = new StringValues(parameter.Value)
+                    select new KeyValuePair<string, StringValues>(parameter.Key, values));
             }
 
             else

src/OpenIddict.Server/OpenIddictServerEvents.Userinfo.cs

@@ -6,6 +6,7 @@
 
 using System.Security.Claims;
 using System.Text.Json;
+using System.Text.Json.Nodes;
 
 namespace OpenIddict.Server;
 
@@ -102,7 +103,7 @@ public static partial class OpenIddictServerEvents
         /// Note: this value should only be populated if the "address"
         /// scope was requested and accepted by the resource owner.
         /// </summary>
-        public JsonElement Address { get; set; }
+        public JsonObject? Address { get; set; }
 
         /// <summary>
         /// Gets or sets the values used for the "aud" claim.

src/OpenIddict.Server/OpenIddictServerHandlers.Discovery.cs

@@ -246,20 +246,20 @@ public static partial class OpenIddictServerHandlers
                     [Metadata.DeviceAuthorizationEndpoint] = notification.DeviceAuthorizationEndpoint?.AbsoluteUri,
                     [Metadata.PushedAuthorizationRequestEndpoint] = notification.PushedAuthorizationEndpoint?.AbsoluteUri,
                     [Metadata.JwksUri] = notification.JsonWebKeySetEndpoint?.AbsoluteUri,
-                    [Metadata.GrantTypesSupported] = notification.GrantTypes.ToArray(),
-                    [Metadata.ResponseTypesSupported] = notification.ResponseTypes.ToArray(),
-                    [Metadata.ResponseModesSupported] = notification.ResponseModes.ToArray(),
-                    [Metadata.ScopesSupported] = notification.Scopes.ToArray(),
-                    [Metadata.ClaimsSupported] = notification.Claims.ToArray(),
-                    [Metadata.IdTokenSigningAlgValuesSupported] = notification.IdTokenSigningAlgorithms.ToArray(),
-                    [Metadata.CodeChallengeMethodsSupported] = notification.CodeChallengeMethods.ToArray(),
-                    [Metadata.SubjectTypesSupported] = notification.SubjectTypes.ToArray(),
-                    [Metadata.PromptValuesSupported] = notification.PromptValues.ToArray(),
-                    [Metadata.TokenEndpointAuthMethodsSupported] = notification.TokenEndpointAuthenticationMethods.ToArray(),
-                    [Metadata.IntrospectionEndpointAuthMethodsSupported] = notification.IntrospectionEndpointAuthenticationMethods.ToArray(),
-                    [Metadata.RevocationEndpointAuthMethodsSupported] = notification.RevocationEndpointAuthenticationMethods.ToArray(),
-                    [Metadata.DeviceAuthorizationEndpointAuthMethodsSupported] = notification.DeviceAuthorizationEndpointAuthenticationMethods.ToArray(),
-                    [Metadata.PushedAuthorizationRequestEndpointAuthMethodsSupported] = notification.PushedAuthorizationEndpointAuthenticationMethods.ToArray(),
+                    [Metadata.GrantTypesSupported] = notification.GrantTypes.ToImmutableArray<string?>(),
+                    [Metadata.ResponseTypesSupported] = notification.ResponseTypes.ToImmutableArray<string?>(),
+                    [Metadata.ResponseModesSupported] = notification.ResponseModes.ToImmutableArray<string?>(),
+                    [Metadata.ScopesSupported] = notification.Scopes.ToImmutableArray<string?>(),
+                    [Metadata.ClaimsSupported] = notification.Claims.ToImmutableArray<string?>(),
+                    [Metadata.IdTokenSigningAlgValuesSupported] = notification.IdTokenSigningAlgorithms.ToImmutableArray<string?>(),
+                    [Metadata.CodeChallengeMethodsSupported] = notification.CodeChallengeMethods.ToImmutableArray<string?>(),
+                    [Metadata.SubjectTypesSupported] = notification.SubjectTypes.ToImmutableArray<string?>(),
+                    [Metadata.PromptValuesSupported] = notification.PromptValues.ToImmutableArray<string?>(),
+                    [Metadata.TokenEndpointAuthMethodsSupported] = notification.TokenEndpointAuthenticationMethods.ToImmutableArray<string?>(),
+                    [Metadata.IntrospectionEndpointAuthMethodsSupported] = notification.IntrospectionEndpointAuthenticationMethods.ToImmutableArray<string?>(),
+                    [Metadata.RevocationEndpointAuthMethodsSupported] = notification.RevocationEndpointAuthenticationMethods.ToImmutableArray<string?>(),
+                    [Metadata.DeviceAuthorizationEndpointAuthMethodsSupported] = notification.DeviceAuthorizationEndpointAuthenticationMethods.ToImmutableArray<string?>(),
+                    [Metadata.PushedAuthorizationRequestEndpointAuthMethodsSupported] = notification.PushedAuthorizationEndpointAuthenticationMethods.ToImmutableArray<string?>(),
                     [Metadata.RequirePushedAuthorizationRequests] = notification.RequirePushedAuthorizationRequests
                 };
 

src/OpenIddict.Server/OpenIddictServerHandlers.Introspection.cs

@@ -268,7 +268,7 @@ public static partial class OpenIddictServerHandlers
                         break;
 
                     default:
-                        response[Claims.Audience] = notification.Audiences.ToArray();
+                        response[Claims.Audience] = notification.Audiences.ToImmutableArray<string?>();
                         break;
                 }
 

src/OpenIddict.Server/OpenIddictServerHandlers.Protection.cs

@@ -556,11 +556,18 @@ public static partial class OpenIddictServerHandlers
                 // Restore the claim destinations from the special oi_cl_dstn claim (represented as a dictionary/JSON object).
                 //
                 // Note: starting in 7.0, Wilson no longer uses JSON.NET and supports a limited set of types for the
-                // TryGetPayloadValue() API. Since ImmutableDictionary<string, string[]> is not supported, the value
-                // is retrieved as a Dictionary<string, string[]>, which is supported by both Wilson 6.x and 7.x.
+                // TryGetPayloadValue() API. Since ImmutableDictionary<string, string[]> is not supported, the value is
+                // retrieved as a Dictionary<string, string[]> and converted to ImmutableDictionary<string, ImmutableArray<string>.
                 if (token.TryGetPayloadValue(Claims.Private.ClaimDestinationsMap, out Dictionary<string, string[]> destinations))
                 {
-                    context.Principal.SetDestinations(destinations.ToImmutableDictionary());
+                    var builder = ImmutableDictionary.CreateBuilder<string, ImmutableArray<string>>();
+
+                    foreach (var destination in destinations)
+                    {
+                        builder.Add(destination.Key, [.. destination.Value]);
+                    }
+
+                    context.Principal.SetDestinations(builder.ToImmutable());
                 }
 
                 context.Logger.LogTrace(SR.GetResourceString(SR.ID6001), context.Token, context.Principal.Claims);

src/OpenIddict.Server/OpenIddictServerHandlers.Userinfo.cs

@@ -243,7 +243,7 @@ public static partial class OpenIddictServerHandlers
                         break;
 
                     default:
-                        response[Claims.Audience] = notification.Audiences.ToArray();
+                        response[Claims.Audience] = notification.Audiences.ToImmutableArray<string?>();
                         break;
                 }
 

src/OpenIddict.Validation.AspNetCore/OpenIddictValidationAspNetCoreHandlers.cs

@@ -7,6 +7,7 @@
 using System.Collections.Immutable;
 using System.ComponentModel;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 using System.Text;
 using System.Text.Json;
 using System.Text.Json.Nodes;
@@ -368,13 +369,17 @@ public static partial class OpenIddictValidationAspNetCoreHandlers
                     context.Parameters[parameter.Key] = parameter.Value switch
                     {
                         OpenIddictParameter value => value,
-                        JsonElement         value => new OpenIddictParameter(value),
-                        JsonNode            value => new OpenIddictParameter(value),
-                        bool                value => new OpenIddictParameter(value),
-                        int                 value => new OpenIddictParameter(value),
-                        long                value => new OpenIddictParameter(value),
-                        string              value => new OpenIddictParameter(value),
-                        string[]            value => new OpenIddictParameter(value),
+
+                        JsonElement             value => new OpenIddictParameter(value),
+                        JsonNode                value => new OpenIddictParameter(value),
+                        bool                    value => new OpenIddictParameter(value),
+                        int                     value => new OpenIddictParameter(value),
+                        long                    value => new OpenIddictParameter(value),
+                        string                  value => new OpenIddictParameter(value),
+                        ImmutableArray<string?> value => new OpenIddictParameter(value),
+
+                        string?[]            value => new(ImmutableCollectionsMarshal.AsImmutableArray(value)),
+                        IEnumerable<string?> value => new OpenIddictParameter([.. value]),
 
                         _ => throw new InvalidOperationException(SR.GetResourceString(SR.ID0115))
                     };

src/OpenIddict.Validation.DataProtection/OpenIddictValidationDataProtectionFormatter.cs

@@ -44,7 +44,7 @@ public sealed class OpenIddictValidationDataProtectionFormatter : IOpenIddictVal
         {
             // Read the version of the format used to serialize the ticket.
             var version = reader.ReadInt32();
-            if (version != 5)
+            if (version is not 5)
             {
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0287));
             }

src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpHandlers.cs

@@ -568,8 +568,8 @@ public static partial class OpenIddictValidationSystemNetHttpHandlers
             {
                 request.RequestUri = OpenIddictHelpers.AddQueryStringParameters(request.RequestUri,
                     context.Transaction.Request.GetParameters().ToDictionary(
-                        parameter => parameter.Key,
-                        parameter => new StringValues((string?[]?) parameter.Value)));
+                        static parameter => parameter.Key,
+                        static parameter => (StringValues) parameter.Value));
             }
 
             // For POST requests, attach the request parameters to the request form by default.
@@ -577,9 +577,9 @@ public static partial class OpenIddictValidationSystemNetHttpHandlers
             {
                 request.Content = new FormUrlEncodedContent(
                     from parameter in context.Transaction.Request.GetParameters()
-                    let values = (string?[]?) parameter.Value
+                    let values = (ImmutableArray<string?>?) parameter.Value
                     where values is not null
-                    from value in values
+                    from value in values.GetValueOrDefault()
                     select new KeyValuePair<string?, string?>(parameter.Key, value));
             }
 

src/OpenIddict.Validation/OpenIddictValidationHandlers.Discovery.cs

@@ -445,24 +445,12 @@ public static partial class OpenIddictValidationHandlers
 
                     // The following parameters MUST be formatted as arrays of objects:
                     JsonWebKeySetParameterNames.Keys => ((JsonElement) value) is JsonElement element &&
-                        element.ValueKind is JsonValueKind.Array && ValidateObjectArray(element),
+                        element.ValueKind is JsonValueKind.Array &&
+                        OpenIddictHelpers.ValidateArrayElements(element, JsonValueKind.Object),
 
                     // Parameters that are not in the well-known list can be of any type.
                     _ => true
                 };
-
-                static bool ValidateObjectArray(JsonElement element)
-                {
-                    foreach (var item in element.EnumerateArray())
-                    {
-                        if (item.ValueKind is not JsonValueKind.Object)
-                        {
-                            return false;
-                        }
-                    }
-
-                    return true;
-                }
             }
         }
 

test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictConverterTests.cs

@@ -269,7 +269,7 @@ public class OpenIddictConverterTests
 
         var message = new OpenIddictMessage();
         message.AddParameter("string", "value");
-        message.AddParameter("array", new[] { "value" });
+        message.AddParameter("array", new OpenIddictParameter(["value"]));
 
         // Act
         converter.Write(writer, value: message, options: null!);

test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictExtensionsTests.cs

@@ -1125,8 +1125,8 @@ public class OpenIddictExtensionsTests
 
         // Assert
         Assert.Equal(2, destinations.Count);
-        Assert.Equal<string[]>([Destinations.AccessToken, Destinations.IdentityToken], destinations[Claims.Name]);
-        Assert.Equal<string[]>([Destinations.IdentityToken], destinations[Claims.Email]);
+        Assert.Equal<string[]>([Destinations.AccessToken, Destinations.IdentityToken], [.. destinations[Claims.Name]]);
+        Assert.Equal<string[]>([Destinations.IdentityToken], [.. destinations[Claims.Email]]);
     }
 
     [Fact]
@@ -1159,8 +1159,8 @@ public class OpenIddictExtensionsTests
 
         // Assert
         Assert.Equal(2, destinations.Count);
-        Assert.Equal<string[]>([Destinations.AccessToken, Destinations.IdentityToken], destinations[Claims.Name]);
-        Assert.Equal<string[]>([Destinations.IdentityToken], destinations[Claims.Email]);
+        Assert.Equal<string[]>([Destinations.AccessToken, Destinations.IdentityToken], [.. destinations[Claims.Name]]);
+        Assert.Equal<string[]>([Destinations.IdentityToken], [.. destinations[Claims.Email]]);
     }
 
     [Fact]
@@ -1192,7 +1192,7 @@ public class OpenIddictExtensionsTests
     {
         // Arrange
         var identity = new ClaimsIdentity();
-        var destinations = (ImmutableDictionary<string, string[]>) null!;
+        var destinations = (ImmutableDictionary<string, ImmutableArray<string>>) null!;
 
         // Act and assert
         var exception = Assert.Throws<ArgumentNullException>(() => identity.SetDestinations(destinations));
@@ -1205,7 +1205,7 @@ public class OpenIddictExtensionsTests
     {
         // Arrange
         var principal = new ClaimsPrincipal(new ClaimsIdentity());
-        var destinations = (ImmutableDictionary<string, string[]>) null!;
+        var destinations = (ImmutableDictionary<string, ImmutableArray<string>>) null!;
 
         // Act and assert
         var exception = Assert.Throws<ArgumentNullException>(() => principal.SetDestinations(destinations));
@@ -1226,7 +1226,7 @@ public class OpenIddictExtensionsTests
 
         var identity = new ClaimsIdentity(claims);
 
-        var destinations = ImmutableDictionary.CreateBuilder<string, string[]>(StringComparer.Ordinal);
+        var destinations = ImmutableDictionary.CreateBuilder<string, ImmutableArray<string>>(StringComparer.Ordinal);
         destinations.Add(Claims.Name, [Destinations.AccessToken, Destinations.IdentityToken]);
         destinations.Add(Claims.Email, [Destinations.IdentityToken]);
         destinations.Add(Claims.Nonce, []);
@@ -1253,7 +1253,7 @@ public class OpenIddictExtensionsTests
 
         var principal = new ClaimsPrincipal(new ClaimsIdentity(claims));
 
-        var destinations = ImmutableDictionary.CreateBuilder<string, string[]>(StringComparer.Ordinal);
+        var destinations = ImmutableDictionary.CreateBuilder<string, ImmutableArray<string>>(StringComparer.Ordinal);
         destinations.Add(Claims.Name, [Destinations.AccessToken, Destinations.IdentityToken]);
         destinations.Add(Claims.Email, [Destinations.IdentityToken]);
         destinations.Add(Claims.Nonce, []);

test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictMessageTests.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Text;
 using System.Text.Encodings.Web;
 using System.Text.Json;
@@ -98,7 +99,8 @@ public class OpenIddictMessageTests
 
         // Assert
         Assert.Equal(1, message.Count);
-        Assert.Equal<string?[]?>(["Fabrikam", "Contoso"], (string?[]?) message.GetParameter("parameter"));
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam", "Contoso"],
+            (ImmutableArray<string?>?) message.GetParameter("parameter"));
     }
 
     [Fact]
@@ -107,12 +109,13 @@ public class OpenIddictMessageTests
         // Arrange and act
         var message = new OpenIddictMessage(
         [
-            new KeyValuePair<string, string?[]?>("parameter", ["Fabrikam", "Contoso"])
+            new KeyValuePair<string, ImmutableArray<string?>?>("parameter", ["Fabrikam", "Contoso"])
         ]);
 
         // Assert
         Assert.Equal(1, message.Count);
-        Assert.Equal<string?[]?>(["Fabrikam", "Contoso"], (string?[]?) message.GetParameter("parameter"));
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam", "Contoso"],
+            (ImmutableArray<string?>?) message.GetParameter("parameter"));
     }
 
     [Fact]
@@ -121,12 +124,12 @@ public class OpenIddictMessageTests
         // Arrange and act
         var message = new OpenIddictMessage(
         [
-            new KeyValuePair<string, string?[]?>("parameter", ["Fabrikam"])
+            new KeyValuePair<string, ImmutableArray<string?>?>("parameter", ["Fabrikam"])
         ]);
 
         // Assert
         Assert.Equal(1, message.Count);
-        Assert.Equal("Fabrikam", message.GetParameter("parameter")?.Value);
+        Assert.Equal("Fabrikam", (string?) message.GetParameter("parameter"));
     }
 
     [Theory]
@@ -423,7 +426,7 @@ public class OpenIddictMessageTests
 
         // Act and assert
         Assert.True(message.TryGetParameter("parameter", out var parameter));
-        Assert.Equal(42, (long?) parameter.Value);
+        Assert.Equal(42, (long?) parameter);
     }
 
     [Fact]
@@ -434,7 +437,7 @@ public class OpenIddictMessageTests
 
         // Act and assert
         Assert.False(message.TryGetParameter("parameter", out OpenIddictParameter parameter));
-        Assert.Null(parameter.Value);
+        Assert.Equal(default, parameter);
     }
 
     [Fact]
@@ -507,7 +510,7 @@ public class OpenIddictMessageTests
         // Arrange
         var message = new OpenIddictMessage
         {
-            ["redirect_uris"] = new[] { "https://abc.org/callback" },
+            ["redirect_uris"] = new OpenIddictParameter(["https://abc.org/callback"]),
             ["client_name"] = "My Example Client"
         };
 

test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictParameterTests.cs

@@ -4,9 +4,12 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
+using System.Runtime.InteropServices;
 using System.Text;
 using System.Text.Json;
 using System.Text.Json.Nodes;
+using Microsoft.Extensions.Primitives;
 using Xunit;
 
 namespace OpenIddict.Abstractions.Tests.Primitives;
@@ -191,9 +194,9 @@ public class OpenIddictParameterTests
         var parameter = new OpenIddictParameter(["Fabrikam", "Contoso"]);
 
         // Act and assert
-        Assert.True(parameter.Equals(new string[] { "Fabrikam", "Contoso" }));
-        Assert.False(parameter.Equals(new string[] { "Fabrikam" }));
-        Assert.False(parameter.Equals(new string[] { "Contoso", "Fabrikam" }));
+        Assert.True(parameter.Equals(new OpenIddictParameter(["Fabrikam", "Contoso"])));
+        Assert.False(parameter.Equals(new OpenIddictParameter(["Fabrikam"])));
+        Assert.False(parameter.Equals(new OpenIddictParameter(["Contoso", "Fabrikam"])));
     }
 
     [Fact]
@@ -203,11 +206,11 @@ public class OpenIddictParameterTests
         var parameter = new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("[0,1,2,3]"));
 
         // Act and assert
-        Assert.True(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("[0,1,2,3]")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("[]")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("[0,1,2]")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("[3,2,1,0]")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("{}")));
+        Assert.True(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("[0,1,2,3]"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("[]"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("[0,1,2]"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("[3,2,1,0]"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("{}"))));
 
         Assert.True(parameter.Equals(new OpenIddictParameter(new JsonArray(0, 1, 2, 3))));
         Assert.False(parameter.Equals(new OpenIddictParameter(new JsonArray())));
@@ -223,11 +226,11 @@ public class OpenIddictParameterTests
         var parameter = new OpenIddictParameter(new JsonArray(0, 1, 2, 3));
 
         // Act and assert
-        Assert.True(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("[0,1,2,3]")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("[]")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("[0,1,2]")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("[3,2,1,0]")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>("{}")));
+        Assert.True(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("[0,1,2,3]"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("[]"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("[0,1,2]"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("[3,2,1,0]"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>("{}"))));
 
         Assert.True(parameter.Equals(new OpenIddictParameter(new JsonArray(0, 1, 2, 3))));
         Assert.False(parameter.Equals(new OpenIddictParameter(new JsonArray())));
@@ -243,11 +246,11 @@ public class OpenIddictParameterTests
         var parameter = new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{""field"":[0,1,2,3]}"));
 
         // Act and assert
-        Assert.True(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"{""field"":[0,1,2,3]}")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"{}")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"{""field"":""value""}")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"{""field"":[0,1,2]}")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"[]")));
+        Assert.True(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{""field"":[0,1,2,3]}"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{}"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{""field"":""value""}"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{""field"":[0,1,2]}"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"[]"))));
 
         Assert.True(parameter.Equals(new OpenIddictParameter(new JsonObject
         {
@@ -285,23 +288,23 @@ public class OpenIddictParameterTests
         });
 
         // Act and assert
-        Assert.True(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"{""field"":[0,1,2,3]}")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"{}")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"{""field"":""value""}")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"{""field"":[0,1,2]}")));
-        Assert.False(parameter.Equals(JsonSerializer.Deserialize<JsonElement>(@"[]")));
+        Assert.True(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{""field"":[0,1,2,3]}"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{}"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{""field"":""value""}"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{""field"":[0,1,2]}"))));
+        Assert.False(parameter.Equals(new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"[]"))));
 
-        Assert.True(parameter.Equals(new JsonObject
+        Assert.True(parameter.Equals(new OpenIddictParameter(new JsonObject
         {
             ["field"] = new JsonArray(0, 1, 2, 3)
-        }));
+        })));
 
-        Assert.False(parameter.Equals(new JsonObject()));
+        Assert.False(parameter.Equals(new OpenIddictParameter(new JsonObject())));
 
-        Assert.False(parameter.Equals(new JsonObject
+        Assert.False(parameter.Equals(new OpenIddictParameter(new JsonObject
         {
             ["field"] = JsonValue.Create("value")
-        }));
+        })));
 
         Assert.False(parameter.Equals(new OpenIddictParameter(new JsonObject
         {
@@ -309,20 +312,20 @@ public class OpenIddictParameterTests
                 @"{""field"":""value""}").GetProperty("field"))
         })));
 
-        Assert.False(parameter.Equals(new JsonObject
+        Assert.False(parameter.Equals(new OpenIddictParameter(new JsonObject
         {
             ["field"] = new JsonArray(0, 1, 2)
-        }));
+        })));
 
-        Assert.True(parameter.Equals(JsonValue.Create(new Dictionary<string, object>
+        Assert.True(parameter.Equals(new OpenIddictParameter(JsonValue.Create(new Dictionary<string, object>
         {
             ["field"] = new JsonArray(0, 1, 2, 3)
-        })));
+        }))));
 
-        Assert.True(parameter.Equals(JsonValue.Create(new Dictionary<string, object>
+        Assert.True(parameter.Equals(new OpenIddictParameter(JsonValue.Create(new Dictionary<string, object>
         {
             ["field"] = new[] { 0, 1, 2, 3 }
-        })));
+        }))));
     }
 
     [Fact]
@@ -797,11 +800,7 @@ public class OpenIddictParameterTests
     public void GetNamedParameters_ReturnsEmptyDictionaryForArrays()
     {
         // Arrange
-        var parameters = new[]
-        {
-            "Fabrikam",
-            "Contoso"
-        };
+        ImmutableArray<string?> parameters = ["Fabrikam", "Contoso"];
 
         var parameter = new OpenIddictParameter(parameters);
 
@@ -924,11 +923,7 @@ public class OpenIddictParameterTests
     public void GetUnnamedParameters_ReturnsExpectedParametersForArrays()
     {
         // Arrange
-        var parameters = new[]
-        {
-            "Fabrikam",
-            "Contoso"
-        };
+        ImmutableArray<string?> parameters = ["Fabrikam", "Contoso"];
 
         var parameter = new OpenIddictParameter(parameters);
 
@@ -1024,7 +1019,7 @@ public class OpenIddictParameterTests
         Assert.True(OpenIddictParameter.IsNullOrEmpty(new OpenIddictParameter((bool?) null)));
         Assert.True(OpenIddictParameter.IsNullOrEmpty(new OpenIddictParameter((long?) null)));
         Assert.True(OpenIddictParameter.IsNullOrEmpty(new OpenIddictParameter((string?) null)));
-        Assert.True(OpenIddictParameter.IsNullOrEmpty(new OpenIddictParameter((string?[]?) null)));
+        Assert.True(OpenIddictParameter.IsNullOrEmpty(new OpenIddictParameter((ImmutableArray<string?>?) null)));
     }
 
     [Fact]
@@ -1502,11 +1497,11 @@ public class OpenIddictParameterTests
     public void BoolConverter_CanCreateParameterFromBooleanValue()
     {
         // Arrange, act and assert
-        Assert.True((bool?) new OpenIddictParameter(true).Value);
-        Assert.True((bool?) new OpenIddictParameter((bool?) true).Value);
+        Assert.True((bool?) new OpenIddictParameter(true));
+        Assert.True((bool?) new OpenIddictParameter((bool?) true));
 
-        Assert.False((bool?) new OpenIddictParameter(false).Value);
-        Assert.False((bool?) new OpenIddictParameter((bool?) false).Value);
+        Assert.False((bool?) new OpenIddictParameter(false));
+        Assert.False((bool?) new OpenIddictParameter((bool?) false));
     }
 
     [Fact]
@@ -1898,8 +1893,8 @@ public class OpenIddictParameterTests
     public void LongConverter_CanCreateParameterFromLongValue()
     {
         // Arrange, act and assert
-        Assert.Equal(42, (long?) new OpenIddictParameter(42).Value);
-        Assert.Equal(42, (long?) new OpenIddictParameter((long?) 42).Value);
+        Assert.Equal(42, (long?) new OpenIddictParameter(42));
+        Assert.Equal(42, (long?) new OpenIddictParameter((long?) 42));
     }
 
     [Fact]
@@ -1970,7 +1965,7 @@ public class OpenIddictParameterTests
     public void StringConverter_CanCreateParameterFromStringValue()
     {
         // Arrange, act and assert
-        Assert.Equal("Fabrikam", (string?) new OpenIddictParameter("Fabrikam").Value);
+        Assert.Equal("Fabrikam", (string?) new OpenIddictParameter("Fabrikam"));
     }
 
     [Fact]
@@ -2041,77 +2036,155 @@ public class OpenIddictParameterTests
     public void StringArrayConverter_CanCreateParameterFromArray()
     {
         // Arrange
-        var array = new[] { "Fabrikam", "Contoso" };
+        string?[] array = ["Fabrikam", "Contoso"];
 
         // Act
-        var parameter = new OpenIddictParameter(array);
+        var parameter = new OpenIddictParameter([.. array]);
 
         // Assert
-        Assert.Same(array, parameter.Value);
+        Assert.Equal<IEnumerable<string?>?>(array, (ImmutableArray<string?>?) parameter);
     }
 
     [Fact]
     public void StringArrayConverter_CanCreateParameterFromPrimitiveValues()
     {
         // Arrange, act and assert
-        Assert.Equal<string?[]?>(["Fabrikam"], (string?[]?) new OpenIddictParameter("Fabrikam"));
-        Assert.Equal<string?[]?>(["false"], (string?[]?) new OpenIddictParameter(false));
-        Assert.Equal<string?[]?>(["42"], (string?[]?) new OpenIddictParameter(42));
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (ImmutableArray<string?>?) new OpenIddictParameter("Fabrikam"));
+        Assert.Equal<IEnumerable<string?>?>(["false"], (ImmutableArray<string?>?) new OpenIddictParameter(false));
+        Assert.Equal<IEnumerable<string?>?>(["42"], (ImmutableArray<string?>?) new OpenIddictParameter(42));
     }
 
     [Fact]
     public void StringArrayConverter_ReturnsDefaultValueForNullValues()
     {
         // Arrange, act and assert
-        Assert.Null((string?[]?) new OpenIddictParameter());
+        Assert.Null((ImmutableArray<string?>?) new OpenIddictParameter());
     }
 
     [Fact]
     public void StringArrayConverter_ReturnsSingleElementArrayForStringValue()
     {
         // Arrange, act and assert
-        Assert.Equal<string?[]?>(["Fabrikam"], (string?[]?) new OpenIddictParameter("Fabrikam"));
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (ImmutableArray<string?>?) new OpenIddictParameter("Fabrikam"));
     }
 
     [Fact]
     public void StringArrayConverter_ReturnsDefaultValueForUnsupportedJsonValues()
     {
         // Arrange, act and assert
-        Assert.Null((string?[]?) new OpenIddictParameter(new JsonElement()));
-        Assert.Null((string?[]?) new OpenIddictParameter(
+        Assert.Null((ImmutableArray<string?>?) new OpenIddictParameter(new JsonElement()));
+        Assert.Null((ImmutableArray<string?>?) new OpenIddictParameter(
             JsonSerializer.Deserialize<JsonElement>(@"[""value"",[]]")));
 
-        Assert.Null((string?[]?) new OpenIddictParameter(
+        Assert.Null((ImmutableArray<string?>?) new OpenIddictParameter(
             JsonSerializer.Deserialize<JsonElement>(@"[""value"",{}]")));
 
-        Assert.Null((string?[]?) new OpenIddictParameter((JsonNode?) null));
-        Assert.Null((string?[]?) new OpenIddictParameter(new JsonArray("value", new JsonArray())));
-        Assert.Null((string?[]?) new OpenIddictParameter(new JsonArray("value", new JsonObject())));
+        Assert.Null((ImmutableArray<string?>?) new OpenIddictParameter((JsonNode?) null));
+        Assert.Null((ImmutableArray<string?>?) new OpenIddictParameter(new JsonArray("value", new JsonArray())));
+        Assert.Null((ImmutableArray<string?>?) new OpenIddictParameter(new JsonArray("value", new JsonObject())));
     }
 
     [Fact]
     public void StringArrayConverter_CanConvertFromJsonValues()
     {
         // Arrange, act and assert
-        Assert.Equal<string?[]?>(["Fabrikam"], (string?[]?) new OpenIddictParameter(
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (ImmutableArray<string?>?) new OpenIddictParameter(
+            JsonSerializer.Deserialize<JsonElement>(@"{""field"":""Fabrikam""}").GetProperty("field")));
+        Assert.Equal<IEnumerable<string?>?>(["false"], (ImmutableArray<string?>?) new OpenIddictParameter(
+            JsonSerializer.Deserialize<JsonElement>(@"{""field"":false}").GetProperty("field")));
+        Assert.Equal<IEnumerable<string?>?>(["42"], (ImmutableArray<string?>?) new OpenIddictParameter(
+            JsonSerializer.Deserialize<JsonElement>(@"{""field"":42}").GetProperty("field")));
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (ImmutableArray<string?>?) new OpenIddictParameter(
+            JsonSerializer.Deserialize<JsonElement>(@"[""Fabrikam""]")));
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) new OpenIddictParameter(
+            JsonSerializer.Deserialize<JsonElement>(@"[""Contoso"",""Fabrikam""]")));
+        Assert.Equal<IEnumerable<string?>?>(["value", "42", "true"], (ImmutableArray<string?>?) new OpenIddictParameter(
+            JsonSerializer.Deserialize<JsonElement>(@"[""value"",42,true]")));
+
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (ImmutableArray<string?>?) new OpenIddictParameter(JsonValue.Create("Fabrikam")));
+        Assert.Equal<IEnumerable<string?>?>(["false"], (ImmutableArray<string?>?) new OpenIddictParameter(JsonValue.Create(false)));
+        Assert.Equal<IEnumerable<string?>?>(["42"], (ImmutableArray<string?>?) new OpenIddictParameter(JsonValue.Create(42)));
+        Assert.Equal<IEnumerable<string?>?>(["42"], (ImmutableArray<string?>?) new OpenIddictParameter(JsonValue.Create(42L)));
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (ImmutableArray<string?>?) new OpenIddictParameter(new JsonArray("Fabrikam")));
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) new OpenIddictParameter(new JsonArray("Contoso", "Fabrikam")));
+        Assert.Equal<IEnumerable<string?>?>(["value", "42", "true"], (ImmutableArray<string?>?) new OpenIddictParameter(new JsonArray("value", 42, true)));
+    }
+
+    [Fact]
+    public void StringValuesConverter_CanCreateParameterFromArray()
+    {
+        // Arrange
+        string?[] array = ["Fabrikam", "Contoso"];
+
+        // Act
+        var parameter = new OpenIddictParameter([.. array]);
+
+        // Assert
+        Assert.Equal<IEnumerable<string?>?>(array, (StringValues?) parameter);
+    }
+
+    [Fact]
+    public void StringValuesConverter_CanCreateParameterFromPrimitiveValues()
+    {
+        // Arrange, act and assert
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (StringValues?) new OpenIddictParameter("Fabrikam"));
+        Assert.Equal<IEnumerable<string?>?>(["false"], (StringValues?) new OpenIddictParameter(false));
+        Assert.Equal<IEnumerable<string?>?>(["42"], (StringValues?) new OpenIddictParameter(42));
+    }
+
+    [Fact]
+    public void StringValuesConverter_ReturnsDefaultValueForNullValues()
+    {
+        // Arrange, act and assert
+        Assert.Null((StringValues?) new OpenIddictParameter());
+    }
+
+    [Fact]
+    public void StringValuesConverter_ReturnsSingleElementArrayForStringValue()
+    {
+        // Arrange, act and assert
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (StringValues?) new OpenIddictParameter("Fabrikam"));
+    }
+
+    [Fact]
+    public void StringValuesConverter_ReturnsDefaultValueForUnsupportedJsonValues()
+    {
+        // Arrange, act and assert
+        Assert.Null((StringValues?) new OpenIddictParameter(new JsonElement()));
+        Assert.Null((StringValues?) new OpenIddictParameter(
+            JsonSerializer.Deserialize<JsonElement>(@"[""value"",[]]")));
+
+        Assert.Null((StringValues?) new OpenIddictParameter(
+            JsonSerializer.Deserialize<JsonElement>(@"[""value"",{}]")));
+
+        Assert.Null((StringValues?) new OpenIddictParameter((JsonNode?) null));
+        Assert.Null((StringValues?) new OpenIddictParameter(new JsonArray("value", new JsonArray())));
+        Assert.Null((StringValues?) new OpenIddictParameter(new JsonArray("value", new JsonObject())));
+    }
+
+    [Fact]
+    public void StringValuesConverter_CanConvertFromJsonValues()
+    {
+        // Arrange, act and assert
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (StringValues?) new OpenIddictParameter(
             JsonSerializer.Deserialize<JsonElement>(@"{""field"":""Fabrikam""}").GetProperty("field")));
-        Assert.Equal<string?[]?>(["false"], (string?[]?) new OpenIddictParameter(
+        Assert.Equal<IEnumerable<string?>?>(["false"], (StringValues?) new OpenIddictParameter(
             JsonSerializer.Deserialize<JsonElement>(@"{""field"":false}").GetProperty("field")));
-        Assert.Equal<string?[]?>(["42"], (string?[]?) new OpenIddictParameter(
+        Assert.Equal<IEnumerable<string?>?>(["42"], (StringValues?) new OpenIddictParameter(
             JsonSerializer.Deserialize<JsonElement>(@"{""field"":42}").GetProperty("field")));
-        Assert.Equal<string?[]?>(["Fabrikam"], (string?[]?) new OpenIddictParameter(
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (StringValues?) new OpenIddictParameter(
             JsonSerializer.Deserialize<JsonElement>(@"[""Fabrikam""]")));
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) new OpenIddictParameter(
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (StringValues?) new OpenIddictParameter(
             JsonSerializer.Deserialize<JsonElement>(@"[""Contoso"",""Fabrikam""]")));
-        Assert.Equal<string?[]?>(["value", "42", "true"], (string?[]?) new OpenIddictParameter(
+        Assert.Equal<IEnumerable<string?>?>(["value", "42", "true"], (StringValues?) new OpenIddictParameter(
             JsonSerializer.Deserialize<JsonElement>(@"[""value"",42,true]")));
 
-        Assert.Equal<string?[]?>(["Fabrikam"], (string?[]?) new OpenIddictParameter(JsonValue.Create("Fabrikam")));
-        Assert.Equal<string?[]?>(["false"], (string?[]?) new OpenIddictParameter(JsonValue.Create(false)));
-        Assert.Equal<string?[]?>(["42"], (string?[]?) new OpenIddictParameter(JsonValue.Create(42)));
-        Assert.Equal<string?[]?>(["42"], (string?[]?) new OpenIddictParameter(JsonValue.Create(42L)));
-        Assert.Equal<string?[]?>(["Fabrikam"], (string?[]?) new OpenIddictParameter(new JsonArray("Fabrikam")));
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) new OpenIddictParameter(new JsonArray("Contoso", "Fabrikam")));
-        Assert.Equal<string?[]?>(["value", "42", "true"], (string?[]?) new OpenIddictParameter(new JsonArray("value", 42, true)));
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (StringValues?) new OpenIddictParameter(JsonValue.Create("Fabrikam")));
+        Assert.Equal<IEnumerable<string?>?>(["false"], (StringValues?) new OpenIddictParameter(JsonValue.Create(false)));
+        Assert.Equal<IEnumerable<string?>?>(["42"], (StringValues?) new OpenIddictParameter(JsonValue.Create(42)));
+        Assert.Equal<IEnumerable<string?>?>(["42"], (StringValues?) new OpenIddictParameter(JsonValue.Create(42L)));
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam"], (StringValues?) new OpenIddictParameter(new JsonArray("Fabrikam")));
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (StringValues?) new OpenIddictParameter(new JsonArray("Contoso", "Fabrikam")));
+        Assert.Equal<IEnumerable<string?>?>(["value", "42", "true"], (StringValues?) new OpenIddictParameter(new JsonArray("value", 42, true)));
     }
 }

test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictRequestTests.cs

@@ -5,7 +5,9 @@
  * the license and the contributors participating to this project.
  */
 
-using System.Text.Json;
+using System.Collections.Immutable;
+using System.Runtime.InteropServices;
+using System.Text.Json.Nodes;
 using Xunit;
 
 namespace OpenIddict.Abstractions.Tests.Primitives;
@@ -48,7 +50,7 @@ public class OpenIddictRequestTests
             {
                 /* property: */ nameof(OpenIddictRequest.Claims),
                 /* name: */ Parameters.Claims,
-                /* value: */ new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{""userinfo"": {}}"))
+                /* value: */ new OpenIddictParameter(JsonObject.Parse(@"{""userinfo"": {}}"))
             };
 
             yield return new object[]
@@ -216,7 +218,7 @@ public class OpenIddictRequestTests
             {
                 /* property: */ nameof(OpenIddictRequest.Registration),
                 /* name: */ Parameters.Registration,
-                /* value: */ new OpenIddictParameter(JsonSerializer.Deserialize<JsonElement>(@"{""policy_uri"": ""http://www.fabrikam.com/policy""}"))
+                /* value: */ new OpenIddictParameter(JsonObject.Parse(@"{""policy_uri"": ""http://www.fabrikam.com/policy""}"))
             };
 
             yield return new object[]
@@ -314,7 +316,16 @@ public class OpenIddictRequestTests
         request.SetParameter(name, value);
 
         // Act and assert
-        Assert.Equal(value.Value, typeof(OpenIddictRequest).GetProperty(property)!.GetValue(request));
+        var info = typeof(OpenIddictRequest).GetProperty(property)!;
+        if (typeof(JsonNode).IsAssignableFrom(info.PropertyType))
+        {
+            Assert.True(JsonNode.DeepEquals((JsonNode?) value.GetRawValue(), (JsonNode?) info.GetValue(request)));
+        }
+
+        else
+        {
+            Assert.Equal(value.GetRawValue(), info.GetValue(request));
+        }
     }
 
     [Theory]
@@ -325,7 +336,16 @@ public class OpenIddictRequestTests
         var request = new OpenIddictRequest();
 
         // Act
-        typeof(OpenIddictRequest).GetProperty(property)!.SetValue(request, value.Value);
+        var info = typeof(OpenIddictRequest).GetProperty(property)!;
+        if (typeof(ImmutableArray<string?>).IsAssignableFrom(info.PropertyType))
+        {
+            info.SetValue(request, ImmutableCollectionsMarshal.AsImmutableArray((string?[]?) value.GetRawValue()));
+        }
+
+        else
+        {
+            info.SetValue(request, value.GetRawValue());
+        }
 
         // Assert
         Assert.Equal(value, request.GetParameter(name));

test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictResponseTests.cs

@@ -5,6 +5,9 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
+using System.Runtime.InteropServices;
+using System.Text.Json.Nodes;
 using Xunit;
 
 namespace OpenIddict.Abstractions.Tests.Primitives;
@@ -145,7 +148,16 @@ public class OpenIddictResponseTests
         response.SetParameter(name, value);
 
         // Act and assert
-        Assert.Equal(value.Value, typeof(OpenIddictResponse).GetProperty(property)!.GetValue(response));
+        var info = typeof(OpenIddictResponse).GetProperty(property)!;
+        if (typeof(JsonNode).IsAssignableFrom(info.PropertyType))
+        {
+            Assert.True(JsonNode.DeepEquals((JsonNode?) value.GetRawValue(), (JsonNode?) info.GetValue(response)));
+        }
+
+        else
+        {
+            Assert.Equal(value.GetRawValue(), info.GetValue(response));
+        }
     }
 
     [Theory]
@@ -156,7 +168,16 @@ public class OpenIddictResponseTests
         var response = new OpenIddictResponse();
 
         // Act
-        typeof(OpenIddictResponse).GetProperty(property)!.SetValue(response, value.Value);
+        var info = typeof(OpenIddictResponse).GetProperty(property)!;
+        if (typeof(ImmutableArray<string?>).IsAssignableFrom(info.PropertyType))
+        {
+            info.SetValue(response, ImmutableCollectionsMarshal.AsImmutableArray((string?[]?) value.GetRawValue()));
+        }
+
+        else
+        {
+            info.SetValue(response, value.GetRawValue());
+        }
 
         // Assert
         Assert.Equal(value, response.GetParameter(name));

test/OpenIddict.Server.AspNetCore.IntegrationTests/OpenIddictServerAspNetCoreIntegrationTests.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Security.Claims;
 using System.Text.Json;
 using System.Text.Json.Nodes;
@@ -257,11 +258,11 @@ public partial class OpenIddictServerAspNetCoreIntegrationTests : OpenIddictServ
         Assert.Equal(JsonValueKind.Number, ((JsonElement) response["integer_parameter"]).ValueKind);
         Assert.Equal("Bob l'Eponge", (string?) response["string_parameter"]);
         Assert.Equal(JsonValueKind.String, ((JsonElement) response["string_parameter"]).ValueKind);
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) response["array_parameter"]);
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["array_parameter"]);
         Assert.Equal(JsonValueKind.Array, ((JsonElement) response["array_parameter"]).ValueKind);
         Assert.Equal("value", (string?) response["object_parameter"]?["parameter"]);
         Assert.Equal(JsonValueKind.Object, ((JsonElement) response["object_parameter"]).ValueKind);
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) response["node_array_parameter"]);
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["node_array_parameter"]);
         Assert.IsType<JsonArray>((JsonNode?) response["node_array_parameter"]);
         Assert.Equal("value", (string?) response["node_object_parameter"]?["parameter"]);
         Assert.IsType<JsonObject>((JsonNode?) response["node_object_parameter"]);
@@ -488,11 +489,11 @@ public partial class OpenIddictServerAspNetCoreIntegrationTests : OpenIddictServ
         Assert.Equal(JsonValueKind.Number, ((JsonElement) response["integer_parameter"]).ValueKind);
         Assert.Equal("Bob l'Eponge", (string?) response["string_parameter"]);
         Assert.Equal(JsonValueKind.String, ((JsonElement) response["string_parameter"]).ValueKind);
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) response["array_parameter"]);
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["array_parameter"]);
         Assert.Equal(JsonValueKind.Array, ((JsonElement) response["array_parameter"]).ValueKind);
         Assert.Equal("value", (string?) response["object_parameter"]?["parameter"]);
         Assert.Equal(JsonValueKind.Object, ((JsonElement) response["object_parameter"]).ValueKind);
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) response["node_array_parameter"]);
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["node_array_parameter"]);
         Assert.IsType<JsonArray>((JsonNode?) response["node_array_parameter"]);
         Assert.Equal("value", (string?) response["node_object_parameter"]?["parameter"]);
         Assert.IsType<JsonObject>((JsonNode?) response["node_object_parameter"]);
@@ -741,8 +742,8 @@ public partial class OpenIddictServerAspNetCoreIntegrationTests : OpenIddictServ
                     }
 
                     var claims = result.Principal.Claims.GroupBy(claim => claim.Type)
-                        .Select(group => new KeyValuePair<string, string?[]?>(
-                            group.Key, group.Select(claim => claim.Value).ToArray()));
+                        .Select(group => new KeyValuePair<string, ImmutableArray<string?>?>(
+                            group.Key, group.Select(claim => claim.Value).ToImmutableArray<string?>()));
 
                     context.Response.ContentType = "application/json";
                     await context.Response.WriteAsync(JsonSerializer.Serialize(new OpenIddictResponse(claims)));

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTestClient.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Net.Http;
 using System.Net.Http.Json;
 using AngleSharp.Html.Parser;
@@ -245,17 +246,17 @@ public class OpenIddictServerIntegrationTestClient : IAsyncDisposable
         {
             message.RequestUri = OpenIddictHelpers.AddQueryStringParameters(message.RequestUri!,
                 request.GetParameters().ToDictionary(
-                    parameter => parameter.Key,
-                    parameter => new StringValues((string?[]?) parameter.Value)));
+                    static parameter => parameter.Key,
+                    static parameter => (StringValues) parameter.Value));
         }
 
         if (message.Method != HttpMethod.Get)
         {
             message.Content = new FormUrlEncodedContent(
                 from parameter in request.GetParameters()
-                let values = (string?[]?) parameter.Value
+                let values = (ImmutableArray<string?>?) parameter.Value
                 where values is not null
-                from value in values
+                from value in values.GetValueOrDefault()
                 select new KeyValuePair<string?, string?>(parameter.Key, value));
         }
 

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.Authentication.cs

@@ -2514,11 +2514,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                         .SetClaim(Claims.Subject, "Bob le Magnifique");
 
                     context.Parameters["custom_parameter"] = "custom_value";
-                    context.Parameters["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Parameters["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -2541,7 +2537,7 @@ public abstract partial class OpenIddictServerIntegrationTests
         Assert.Null(response.ErrorUri);
         Assert.NotNull(response.AccessToken);
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 
     [Theory]
@@ -2660,11 +2656,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -2683,7 +2675,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 
     [Fact]
@@ -5204,11 +5196,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Parameters["custom_parameter"] = "custom_value";
-                    context.Parameters["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Parameters["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -5231,7 +5219,7 @@ public abstract partial class OpenIddictServerIntegrationTests
         Assert.Null(response.ErrorUri);
         Assert.NotNull(response.RequestUri);
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 
     [Fact]
@@ -5283,11 +5271,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -5306,6 +5290,6 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 }

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.Device.cs

@@ -1027,11 +1027,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                     context.Principal = new ClaimsPrincipal(new ClaimsIdentity());
 
                     context.Parameters["custom_parameter"] = "custom_value";
-                    context.Parameters["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Parameters["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -1051,7 +1047,7 @@ public abstract partial class OpenIddictServerIntegrationTests
         Assert.Null(response.ErrorUri);
         Assert.NotNull(response.DeviceCode);
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 
     [Fact]
@@ -1116,11 +1112,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -1136,7 +1128,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 
     [Theory]
@@ -1467,11 +1459,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                         .SetClaim(Claims.Subject, "Bob le Magnifique");
 
                     context.Parameters["custom_parameter"] = "custom_value";
-                    context.Parameters["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Parameters["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -1496,7 +1484,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 
     [Fact]

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.Discovery.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Net.Http;
 using System.Security.Cryptography;
 using System.Text.Json;
@@ -423,11 +424,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var methods = (string?[]?) response[Metadata.TokenEndpointAuthMethodsSupported];
+        var methods = (ImmutableArray<string?>?) response[Metadata.TokenEndpointAuthMethodsSupported];
 
         // Assert
         Assert.NotNull(methods);
-        Assert.Equal(3, methods.Length);
+        Assert.Equal(3, methods.Value.Length);
         Assert.Contains(ClientAuthenticationMethods.ClientSecretPost, methods);
         Assert.Contains(ClientAuthenticationMethods.PrivateKeyJwt, methods);
         Assert.Contains("custom", methods);
@@ -465,11 +466,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var methods = (string?[]?) response[Metadata.IntrospectionEndpointAuthMethodsSupported];
+        var methods = (ImmutableArray<string?>?) response[Metadata.IntrospectionEndpointAuthMethodsSupported];
 
         // Assert
         Assert.NotNull(methods);
-        Assert.Equal(3, methods.Length);
+        Assert.Equal(3, methods.Value.Length);
         Assert.Contains(ClientAuthenticationMethods.ClientSecretPost, methods);
         Assert.Contains(ClientAuthenticationMethods.PrivateKeyJwt, methods);
         Assert.Contains("custom", methods);
@@ -507,11 +508,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var methods = (string?[]?) response[Metadata.RevocationEndpointAuthMethodsSupported];
+        var methods = (ImmutableArray<string?>?) response[Metadata.RevocationEndpointAuthMethodsSupported];
 
         // Assert
         Assert.NotNull(methods);
-        Assert.Equal(3, methods.Length);
+        Assert.Equal(3, methods.Value.Length);
         Assert.Contains(ClientAuthenticationMethods.ClientSecretPost, methods);
         Assert.Contains(ClientAuthenticationMethods.PrivateKeyJwt, methods);
         Assert.Contains("custom", methods);
@@ -550,11 +551,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var methods = (string?[]?) response[Metadata.DeviceAuthorizationEndpointAuthMethodsSupported];
+        var methods = (ImmutableArray<string?>?) response[Metadata.DeviceAuthorizationEndpointAuthMethodsSupported];
 
         // Assert
         Assert.NotNull(methods);
-        Assert.Equal(3, methods.Length);
+        Assert.Equal(3, methods.Value.Length);
         Assert.Contains(ClientAuthenticationMethods.ClientSecretPost, methods);
         Assert.Contains(ClientAuthenticationMethods.PrivateKeyJwt, methods);
         Assert.Contains("custom", methods);
@@ -592,11 +593,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var methods = (string?[]?) response[Metadata.PushedAuthorizationRequestEndpointAuthMethodsSupported];
+        var methods = (ImmutableArray<string?>?) response[Metadata.PushedAuthorizationRequestEndpointAuthMethodsSupported];
 
         // Assert
         Assert.NotNull(methods);
-        Assert.Equal(3, methods.Length);
+        Assert.Equal(3, methods.Value.Length);
         Assert.Contains(ClientAuthenticationMethods.ClientSecretPost, methods);
         Assert.Contains(ClientAuthenticationMethods.PrivateKeyJwt, methods);
         Assert.Contains("custom", methods);
@@ -617,11 +618,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var types = (string?[]?) response[Metadata.GrantTypesSupported];
+        var types = (ImmutableArray<string?>?) response[Metadata.GrantTypesSupported];
 
         // Assert
         Assert.NotNull(types);
-        Assert.Equal(2, types.Length);
+        Assert.Equal(2, types.Value.Length);
         Assert.Contains(GrantTypes.AuthorizationCode, types);
         Assert.Contains(GrantTypes.Password, types);
     }
@@ -659,11 +660,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var methods = (string?[]?) response[Metadata.CodeChallengeMethodsSupported];
+        var methods = (ImmutableArray<string?>?) response[Metadata.CodeChallengeMethodsSupported];
 
         // Assert
         Assert.NotNull(methods);
-        Assert.Equal(2, methods.Length);
+        Assert.Equal(2, methods.Value.Length);
         Assert.Contains(CodeChallengeMethods.Sha256, methods);
         Assert.Contains(CodeChallengeMethods.Plain, methods);
     }
@@ -701,11 +702,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var modes = (string?[]?) response[Metadata.ResponseModesSupported];
+        var modes = (ImmutableArray<string?>?) response[Metadata.ResponseModesSupported];
 
         // Assert
         Assert.NotNull(modes);
-        Assert.Equal(2, modes.Length);
+        Assert.Equal(2, modes.Value.Length);
         Assert.Contains(ResponseModes.FormPost, modes);
         Assert.Contains(ResponseModes.Fragment, modes);
     }
@@ -743,11 +744,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var types = (string?[]?) response[Metadata.ResponseTypesSupported];
+        var types = (ImmutableArray<string?>?) response[Metadata.ResponseTypesSupported];
 
         // Assert
         Assert.NotNull(types);
-        Assert.Equal(2, types.Length);
+        Assert.Equal(2, types.Value.Length);
         Assert.Contains(ResponseTypes.Code, types);
         Assert.Contains(ResponseTypes.Code + ' ' + ResponseTypes.IdToken, types);
     }
@@ -785,11 +786,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var scopes = (string?[]?) response[Metadata.ScopesSupported];
+        var scopes = (ImmutableArray<string?>?) response[Metadata.ScopesSupported];
 
         // Assert
         Assert.NotNull(scopes);
-        Assert.Equal(2, scopes.Length);
+        Assert.Equal(2, scopes.Value.Length);
         Assert.Contains(Scopes.OpenId, scopes);
         Assert.Contains("custom_scope", scopes);
     }
@@ -827,11 +828,11 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var claims = (string?[]?) response[Metadata.ClaimsSupported];
+        var claims = (ImmutableArray<string?>?) response[Metadata.ClaimsSupported];
 
         // Assert
         Assert.NotNull(claims);
-        Assert.Equal(2, claims.Length);
+        Assert.Equal(2, claims.Value.Length);
         Assert.Contains(Claims.Profile, claims);
         Assert.Contains("custom_claim", claims);
     }
@@ -850,7 +851,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var types = (string?[]?) response[Metadata.SubjectTypesSupported];
+        var types = (ImmutableArray<string?>?) response[Metadata.SubjectTypesSupported];
 
         // Assert
         Assert.NotNull(types);
@@ -874,7 +875,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var types = (string?[]?) response[Metadata.PromptValuesSupported];
+        var types = (ImmutableArray<string?>?) response[Metadata.PromptValuesSupported];
 
         // Assert
         Assert.NotNull(types);
@@ -905,7 +906,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var algorithms = (string?[]?) response[Metadata.IdTokenSigningAlgValuesSupported];
+        var algorithms = (ImmutableArray<string?>?) response[Metadata.IdTokenSigningAlgValuesSupported];
 
         // Assert
         Assert.NotNull(algorithms);
@@ -927,7 +928,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var algorithms = (string?[]?) response[Metadata.IdTokenSigningAlgValuesSupported];
+        var algorithms = (ImmutableArray<string?>?) response[Metadata.IdTokenSigningAlgValuesSupported];
 
         // Assert
         Assert.NotNull(algorithms);
@@ -953,7 +954,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Act
         var response = await client.GetAsync("/.well-known/openid-configuration");
-        var algorithms = (string?[]?) response[Metadata.IdTokenSigningAlgValuesSupported];
+        var algorithms = (ImmutableArray<string?>?) response[Metadata.IdTokenSigningAlgValuesSupported];
 
         // Assert
         Assert.NotNull(algorithms);
@@ -1131,11 +1132,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -1629,11 +1626,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -1646,6 +1639,6 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 }

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.Exchange.cs

@@ -4258,11 +4258,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                         .SetClaim(Claims.Subject, "Bob le Magnifique");
 
                     context.Parameters["custom_parameter"] = "custom_value";
-                    context.Parameters["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Parameters["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -4284,7 +4280,7 @@ public abstract partial class OpenIddictServerIntegrationTests
         Assert.Null(response.ErrorUri);
         Assert.NotNull(response.AccessToken);
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 
     [Fact]
@@ -4353,11 +4349,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -4375,6 +4367,6 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 }

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.Introspection.cs

@@ -1048,7 +1048,7 @@ public abstract partial class OpenIddictServerIntegrationTests
         Assert.Equal(JsonValueKind.True, ((JsonElement) response["boolean_claim"]).ValueKind);
         Assert.Equal(42, (long) response["integer_claim"]);
         Assert.Equal(JsonValueKind.Number, ((JsonElement) response["integer_claim"]).ValueKind);
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) response["array_claim"]);
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["array_claim"]);
         Assert.Equal(JsonValueKind.Array, ((JsonElement) response["array_claim"]).ValueKind);
         Assert.Equal("value", (string?) response["object_claim"]?["parameter"]);
         Assert.Equal(JsonValueKind.Object, ((JsonElement) response["object_claim"]).ValueKind);
@@ -1815,11 +1815,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -1835,6 +1831,6 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 }

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.Protection.cs

@@ -316,8 +316,8 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("Bob le Magnifique", (string?) response[Claims.Subject]);
-        Assert.Equal<string?[]?>(["Fabrikam", "Contoso"], (string?[]?) response[Claims.Audience]);
-        Assert.Equal<string?[]?>(["Fabrikam", "Contoso"], (string?[]?) response[Claims.Private.Audience]);
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam", "Contoso"], (ImmutableArray<string?>?) response[Claims.Audience]);
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam", "Contoso"], (ImmutableArray<string?>?) response[Claims.Private.Audience]);
     }
 
     [Fact]
@@ -415,7 +415,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("Bob le Magnifique", (string?) response[Claims.Subject]);
-        Assert.Equal<string?[]?>([Scopes.OpenId, Scopes.Profile], (string?[]?) response[Claims.Private.Scope]);
+        Assert.Equal<IEnumerable<string?>?>([Scopes.OpenId, Scopes.Profile], (ImmutableArray<string?>?) response[Claims.Private.Scope]);
     }
 
     [Fact]
@@ -464,7 +464,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("Bob le Magnifique", (string?) response[Claims.Subject]);
-        Assert.Equal<string?[]?>([Scopes.OpenId, Scopes.Profile], (string?[]?) response[Claims.Private.Scope]);
+        Assert.Equal<IEnumerable<string?>?>([Scopes.OpenId, Scopes.Profile], (ImmutableArray<string?>?) response[Claims.Private.Scope]);
     }
 
     [Fact]

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.Revocation.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Net.Http;
 using System.Security.Claims;
 using Microsoft.Extensions.DependencyInjection;
@@ -1146,11 +1147,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -1166,6 +1163,6 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 }

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.Session.cs

@@ -1044,11 +1044,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                     context.SignOut();
 
                     context.Parameters["custom_parameter"] = "custom_value";
-                    context.Parameters["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Parameters["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -1064,7 +1060,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 
     [Fact]
@@ -1126,11 +1122,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -1146,7 +1138,7 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 
     [Fact]

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.Userinfo.cs

@@ -387,7 +387,7 @@ public abstract partial class OpenIddictServerIntegrationTests
         Assert.Equal(3, response.Count);
         Assert.Equal("http://localhost/", (string?) response[Claims.Issuer]);
         Assert.Equal("Bob le Magnifique", (string?) response[Claims.Subject]);
-        Assert.Equal<string?[]?>(["Fabrikam", "Contoso"], (string?[]?) response[Claims.Audience]);
+        Assert.Equal<IEnumerable<string?>?>(["Fabrikam", "Contoso"], (ImmutableArray<string?>?) response[Claims.Audience]);
     }
 
     [Fact]
@@ -788,11 +788,7 @@ public abstract partial class OpenIddictServerIntegrationTests
                 builder.UseInlineHandler(context =>
                 {
                     context.Response["custom_parameter"] = "custom_value";
-                    context.Response["parameter_with_multiple_values"] = new[]
-                    {
-                        "custom_value_1",
-                        "custom_value_2"
-                    };
+                    context.Response["parameter_with_multiple_values"] = new(["custom_value_1", "custom_value_2"]);
 
                     return default;
                 }));
@@ -808,6 +804,6 @@ public abstract partial class OpenIddictServerIntegrationTests
 
         // Assert
         Assert.Equal("custom_value", (string?) response["custom_parameter"]);
-        Assert.Equal<string?[]?>(["custom_value_1", "custom_value_2"], (string?[]?) response["parameter_with_multiple_values"]);
+        Assert.Equal<IEnumerable<string?>?>(["custom_value_1", "custom_value_2"], (ImmutableArray<string?>?) response["parameter_with_multiple_values"]);
     }
 }

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTests.cs

@@ -1456,11 +1456,11 @@ public abstract partial class OpenIddictServerIntegrationTests
         Assert.Equal(JsonValueKind.Number, ((JsonElement) response["integer_parameter"]).ValueKind);
         Assert.Equal("Bob l'Eponge", (string?) response["string_parameter"]);
         Assert.Equal(JsonValueKind.String, ((JsonElement) response["string_parameter"]).ValueKind);
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) response["array_parameter"]);
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["array_parameter"]);
         Assert.Equal(JsonValueKind.Array, ((JsonElement) response["array_parameter"]).ValueKind);
         Assert.Equal("value", (string?) response["object_parameter"]?["parameter"]);
         Assert.Equal(JsonValueKind.Object, ((JsonElement) response["object_parameter"]).ValueKind);
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) response["node_array_parameter"]);
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["node_array_parameter"]);
         Assert.IsType<JsonArray>((JsonNode?) response["node_array_parameter"]);
         Assert.Equal("value", (string?) response["node_object_parameter"]?["parameter"]);
         Assert.IsType<JsonObject>((JsonNode?) response["node_object_parameter"]);
@@ -3899,11 +3899,11 @@ public abstract partial class OpenIddictServerIntegrationTests
         Assert.Equal(JsonValueKind.Number, ((JsonElement) response["integer_parameter"]).ValueKind);
         Assert.Equal("Bob l'Eponge", (string?) response["string_parameter"]);
         Assert.Equal(JsonValueKind.String, ((JsonElement) response["string_parameter"]).ValueKind);
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) response["array_parameter"]);
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["array_parameter"]);
         Assert.Equal(JsonValueKind.Array, ((JsonElement) response["array_parameter"]).ValueKind);
         Assert.Equal("value", (string?) response["object_parameter"]?["parameter"]);
         Assert.Equal(JsonValueKind.Object, ((JsonElement) response["object_parameter"]).ValueKind);
-        Assert.Equal<string?[]?>(["Contoso", "Fabrikam"], (string?[]?) response["node_array_parameter"]);
+        Assert.Equal<IEnumerable<string?>?>(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["node_array_parameter"]);
         Assert.IsType<JsonArray>((JsonNode?) response["node_array_parameter"]);
         Assert.Equal("value", (string?) response["node_object_parameter"]?["parameter"]);
         Assert.IsType<JsonObject>((JsonNode?) response["node_object_parameter"]);

test/OpenIddict.Server.Owin.IntegrationTests/OpenIddictServerOwinIntegrationTests.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Security.Claims;
 using System.Text.Json;
 using Microsoft.Extensions.DependencyInjection;
@@ -254,7 +255,7 @@ public partial class OpenIddictServerOwinIntegrationTests : OpenIddictServerInte
         Assert.Equal(JsonValueKind.Number, ((JsonElement) response["integer_parameter"]).ValueKind);
         Assert.Equal("Bob l'Eponge", (string?) response["string_parameter"]);
         Assert.Equal(JsonValueKind.String, ((JsonElement) response["string_parameter"]).ValueKind);
-        Assert.Equal(["Contoso", "Fabrikam"], (string?[]?) response["json_parameter"]);
+        Assert.Equal(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["json_parameter"]);
         Assert.Equal(JsonValueKind.Array, ((JsonElement) response["json_parameter"]).ValueKind);
     }
 
@@ -479,7 +480,7 @@ public partial class OpenIddictServerOwinIntegrationTests : OpenIddictServerInte
         Assert.Equal(JsonValueKind.Number, ((JsonElement) response["integer_parameter"]).ValueKind);
         Assert.Equal("Bob l'Eponge", (string?) response["string_parameter"]);
         Assert.Equal(JsonValueKind.String, ((JsonElement) response["string_parameter"]).ValueKind);
-        Assert.Equal(["Contoso", "Fabrikam"], (string?[]?) response["json_parameter"]);
+        Assert.Equal(["Contoso", "Fabrikam"], (ImmutableArray<string?>?) response["json_parameter"]);
         Assert.Equal(JsonValueKind.Array, ((JsonElement) response["json_parameter"]).ValueKind);
     }
 
@@ -697,8 +698,8 @@ public partial class OpenIddictServerOwinIntegrationTests : OpenIddictServerInte
                     }
 
                     var claims = result.Identity.Claims.GroupBy(claim => claim.Type)
-                        .Select(group => new KeyValuePair<string, string?[]?>(
-                            group.Key, group.Select(claim => claim.Value).ToArray()));
+                        .Select(group => new KeyValuePair<string, ImmutableArray<string?>?>(
+                            group.Key, group.Select(claim => claim.Value).ToImmutableArray<string?>()));
 
                     context.Response.ContentType = "application/json";
                     await context.Response.WriteAsync(JsonSerializer.Serialize(new OpenIddictResponse(claims)));

test/OpenIddict.Validation.AspNetCore.IntegrationTests/OpenIddictValidationAspNetCoreIntegrationTests.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Security.Claims;
 using System.Text.Json;
 using Microsoft.AspNetCore.Authentication;
@@ -184,8 +185,8 @@ public partial class OpenIddictValidationAspNetCoreIntegrationTests : OpenIddict
                     }
 
                     var claims = result.Principal.Claims.GroupBy(claim => claim.Type)
-                        .Select(group => new KeyValuePair<string, string?[]?>(
-                            group.Key, group.Select(claim => claim.Value).ToArray()));
+                        .Select(group => new KeyValuePair<string, ImmutableArray<string?>?>(
+                            group.Key, group.Select(claim => claim.Value).ToImmutableArray<string?>()));
 
                     context.Response.ContentType = "application/json";
                     await context.Response.WriteAsync(JsonSerializer.Serialize(new OpenIddictResponse(claims)));

test/OpenIddict.Validation.IntegrationTests/OpenIddictValidationIntegrationTestClient.cs

@@ -4,8 +4,10 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Net.Http;
 using System.Net.Http.Json;
+using System.Runtime.InteropServices;
 using AngleSharp.Html.Parser;
 using Microsoft.Extensions.Primitives;
 using OpenIddict.Extensions;
@@ -245,17 +247,17 @@ public class OpenIddictValidationIntegrationTestClient : IAsyncDisposable
         {
             message.RequestUri = OpenIddictHelpers.AddQueryStringParameters(message.RequestUri!,
                 request.GetParameters().ToDictionary(
-                    parameter => parameter.Key,
-                    parameter => new StringValues((string?[]?) parameter.Value)));
+                    static parameter => parameter.Key,
+                    static parameter => (StringValues) parameter.Value));
         }
 
         if (message.Method != HttpMethod.Get)
         {
             message.Content = new FormUrlEncodedContent(
                 from parameter in request.GetParameters()
-                let values = (string?[]?) parameter.Value
+                let values = (ImmutableArray<string?>?) parameter.Value
                 where values is not null
-                from value in values
+                from value in values.GetValueOrDefault()
                 select new KeyValuePair<string?, string?>(parameter.Key, value));
         }
 

test/OpenIddict.Validation.Owin.IntegrationTests/OpenIddictValidationOwinIntegrationTests.cs

@@ -4,6 +4,7 @@
  * the license and the contributors participating to this project.
  */
 
+using System.Collections.Immutable;
 using System.Security.Claims;
 using System.Text.Json;
 using Microsoft.Extensions.DependencyInjection;
@@ -169,8 +170,8 @@ public partial class OpenIddictValidationOwinIntegrationTests : OpenIddictValida
                     }
 
                     var claims = result.Identity.Claims.GroupBy(claim => claim.Type)
-                        .Select(group => new KeyValuePair<string, string?[]?>(
-                            group.Key, group.Select(claim => claim.Value).ToArray()));
+                        .Select(group => new KeyValuePair<string, ImmutableArray<string?>?>(
+                            group.Key, group.Select(claim => claim.Value).ToImmutableArray<string?>()));
 
                     context.Response.ContentType = "application/json";
                     await context.Response.WriteAsync(JsonSerializer.Serialize(new OpenIddictResponse(claims)));