Declare OpenIddictClientRegistration.ConfigurationManager as a nullable property

src/OpenIddict.Abstractions/OpenIddictResources.resx

@@ -1572,6 +1572,9 @@ To apply post-logout redirection responses, create a class implementing 'IOpenId
   <data name="ID0421" xml:space="preserve">
     <value>At least one subject type must be supported.</value>
   </data>
+  <data name="ID0422" xml:space="preserve">
+    <value>A configuration manager must be attached to the client registration to be able to resolve the server configuration.</value>
+  </data>
   <data name="ID2000" xml:space="preserve">
     <value>The security token is missing.</value>
   </data>

src/OpenIddict.Client/OpenIddictClientHandlers.Protection.cs

@@ -305,7 +305,8 @@ public static partial class OpenIddictClientHandlers
                     // If validation failed because of an unrecognized key identifier and a client
                     // registration is available, inform the configuration manager that the configuration
                     // MAY have be refreshed by sending a new discovery request to the authorization server.
-                    if (context.Registration is not null && result.Exception is SecurityTokenSignatureKeyNotFoundException)
+                    if (result.Exception is SecurityTokenSignatureKeyNotFoundException &&
+                        context.Registration.ConfigurationManager is not null)
                     {
                         context.Registration.ConfigurationManager.RequestRefresh();
                     }

src/OpenIddict.Client/OpenIddictClientHandlers.cs

@@ -423,26 +423,34 @@ public static partial class OpenIddictClientHandlers
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0408));
             }
 
-            try
+            // Resolve and attach the server configuration to the context if none has been set already.
+            if (context.Configuration is null)
             {
-                // Resolve and attach the server configuration to the context if none has been set already.
-                context.Configuration ??= await context.Registration.ConfigurationManager
-                    .GetConfigurationAsync(context.CancellationToken)
-                    .WaitAsync(context.CancellationToken) ??
-                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0140));
-            }
+                if (context.Registration.ConfigurationManager is null)
+                {
+                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0422));
+                }
 
-            catch (Exception exception) when (!OpenIddictHelpers.IsFatal(exception) &&
-                exception is not OperationCanceledException)
-            {
-                context.Logger.LogError(exception, SR.GetResourceString(SR.ID6219));
+                try
+                {
+                    context.Configuration = await context.Registration.ConfigurationManager
+                        .GetConfigurationAsync(context.CancellationToken)
+                        .WaitAsync(context.CancellationToken) ??
+                        throw new InvalidOperationException(SR.GetResourceString(SR.ID0140));
+                }
 
-                context.Reject(
-                    error: Errors.ServerError,
-                    description: SR.GetResourceString(SR.ID2170),
-                    uri: SR.FormatID8000(SR.ID2170));
+                catch (Exception exception) when (!OpenIddictHelpers.IsFatal(exception) &&
+                    exception is not OperationCanceledException)
+                {
+                    context.Logger.LogError(exception, SR.GetResourceString(SR.ID6219));
 
-                return;
+                    context.Reject(
+                        error: Errors.ServerError,
+                        description: SR.GetResourceString(SR.ID2170),
+                        uri: SR.FormatID8000(SR.ID2170));
+
+                    return;
+                }
             }
 
             // Ensure the selected grant type, if explicitly set, is listed as supported in the configuration.
@@ -1019,28 +1027,37 @@ public static partial class OpenIddictClientHandlers
             // Note: if the static registration cannot be found in the options, this may indicate
             // the client was removed after the authorization dance started and thus, can no longer
             // be used to authenticate users. In this case, throw an exception to abort the flow.
-            context.Registration = await _service.GetClientRegistrationByIdAsync(context.RegistrationId, context.CancellationToken);
+            context.Registration ??= await _service.GetClientRegistrationByIdAsync(context.RegistrationId, context.CancellationToken);
 
-            try
+            // Resolve and attach the server configuration to the context if none has been set already.
+            if (context.Configuration is null)
             {
-                // Resolve and attach the server configuration to the context.
-                context.Configuration = await context.Registration.ConfigurationManager
-                    .GetConfigurationAsync(context.CancellationToken)
-                    .WaitAsync(context.CancellationToken) ??
-                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0140));
-            }
+                if (context.Registration.ConfigurationManager is null)
+                {
+                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0422));
+                }
 
-            catch (Exception exception) when (!OpenIddictHelpers.IsFatal(exception) &&
-                exception is not OperationCanceledException)
-            {
-                context.Logger.LogError(exception, SR.GetResourceString(SR.ID6219));
+                try
+                {
+                    // Resolve and attach the server configuration to the context.
+                    context.Configuration = await context.Registration.ConfigurationManager
+                        .GetConfigurationAsync(context.CancellationToken)
+                        .WaitAsync(context.CancellationToken) ??
+                        throw new InvalidOperationException(SR.GetResourceString(SR.ID0140));
+                }
 
-                context.Reject(
-                    error: Errors.ServerError,
-                    description: SR.GetResourceString(SR.ID2170),
-                    uri: SR.FormatID8000(SR.ID2170));
+                catch (Exception exception) when (!OpenIddictHelpers.IsFatal(exception) &&
+                    exception is not OperationCanceledException)
+                {
+                    context.Logger.LogError(exception, SR.GetResourceString(SR.ID6219));
 
-                return;
+                    context.Reject(
+                        error: Errors.ServerError,
+                        description: SR.GetResourceString(SR.ID2170),
+                        uri: SR.FormatID8000(SR.ID2170));
+
+                    return;
+                }
             }
         }
     }
@@ -4209,26 +4226,34 @@ public static partial class OpenIddictClientHandlers
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0408));
             }
 
-            try
+            // Resolve and attach the server configuration to the context if none has been set already.
+            if (context.Configuration is null)
             {
-                // Resolve and attach the server configuration to the context if none has been set already.
-                context.Configuration ??= await context.Registration.ConfigurationManager
-                    .GetConfigurationAsync(context.CancellationToken)
-                    .WaitAsync(context.CancellationToken) ??
-                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0140));
-            }
+                if (context.Registration.ConfigurationManager is null)
+                {
+                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0422));
+                }
 
-            catch (Exception exception) when (!OpenIddictHelpers.IsFatal(exception) &&
-                exception is not OperationCanceledException)
-            {
-                context.Logger.LogError(exception, SR.GetResourceString(SR.ID6219));
+                try
+                {
+                    context.Configuration = await context.Registration.ConfigurationManager
+                        .GetConfigurationAsync(context.CancellationToken)
+                        .WaitAsync(context.CancellationToken) ??
+                        throw new InvalidOperationException(SR.GetResourceString(SR.ID0140));
+                }
 
-                context.Reject(
-                    error: Errors.ServerError,
-                    description: SR.GetResourceString(SR.ID2170),
-                    uri: SR.FormatID8000(SR.ID2170));
+                catch (Exception exception) when (!OpenIddictHelpers.IsFatal(exception) &&
+                    exception is not OperationCanceledException)
+                {
+                    context.Logger.LogError(exception, SR.GetResourceString(SR.ID6219));
 
-                return;
+                    context.Reject(
+                        error: Errors.ServerError,
+                        description: SR.GetResourceString(SR.ID2170),
+                        uri: SR.FormatID8000(SR.ID2170));
+
+                    return;
+                }
             }
         }
     }
@@ -5852,26 +5877,34 @@ public static partial class OpenIddictClientHandlers
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0408));
             }
 
-            try
+            // Resolve and attach the server configuration to the context if none has been set already.
+            if (context.Configuration is null)
             {
-                // Resolve and attach the server configuration to the context if none has been set already.
-                context.Configuration ??= await context.Registration.ConfigurationManager
-                    .GetConfigurationAsync(context.CancellationToken)
-                    .WaitAsync(context.CancellationToken) ??
-                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0140));
-            }
+                if (context.Registration.ConfigurationManager is null)
+                {
+                    throw new InvalidOperationException(SR.GetResourceString(SR.ID0422));
+                }
 
-            catch (Exception exception) when (!OpenIddictHelpers.IsFatal(exception) &&
-                exception is not OperationCanceledException)
-            {
-                context.Logger.LogError(exception, SR.GetResourceString(SR.ID6219));
+                try
+                {
+                    context.Configuration = await context.Registration.ConfigurationManager
+                        .GetConfigurationAsync(context.CancellationToken)
+                        .WaitAsync(context.CancellationToken) ??
+                        throw new InvalidOperationException(SR.GetResourceString(SR.ID0140));
+                }
 
-                context.Reject(
-                    error: Errors.ServerError,
-                    description: SR.GetResourceString(SR.ID2170),
-                    uri: SR.FormatID8000(SR.ID2170));
+                catch (Exception exception) when (!OpenIddictHelpers.IsFatal(exception) &&
+                    exception is not OperationCanceledException)
+                {
+                    context.Logger.LogError(exception, SR.GetResourceString(SR.ID6219));
 
-                return;
+                    context.Reject(
+                        error: Errors.ServerError,
+                        description: SR.GetResourceString(SR.ID2170),
+                        uri: SR.FormatID8000(SR.ID2170));
+
+                    return;
+                }
             }
         }
     }

src/OpenIddict.Client/OpenIddictClientRegistration.cs

@@ -143,7 +143,7 @@ public sealed class OpenIddictClientRegistration
     /// <summary>
     /// Gets or sets the configuration manager used to retrieve and cache the server configuration.
     /// </summary>
-    public IConfigurationManager<OpenIddictConfiguration> ConfigurationManager { get; set; } = default!;
+    public IConfigurationManager<OpenIddictConfiguration>? ConfigurationManager { get; set; }
 
     /// <summary>
     /// Gets or sets the URI of the configuration endpoint exposed by the server.

src/OpenIddict.Client/OpenIddictClientService.cs

@@ -154,6 +154,11 @@ public sealed class OpenIddictClientService
         }
 
         var registration = await GetClientRegistrationAsync(issuer, cancellationToken);
+        if (registration.ConfigurationManager is null)
+        {
+            throw new InvalidOperationException(SR.GetResourceString(SR.ID0422));
+        }
+
         return await registration.ConfigurationManager
             .GetConfigurationAsync(cancellationToken)
             .WaitAsync(cancellationToken) ??
@@ -182,6 +187,11 @@ public sealed class OpenIddictClientService
         }
 
         var registration = await GetClientRegistrationAsync(provider, cancellationToken);
+        if (registration.ConfigurationManager is null)
+        {
+            throw new InvalidOperationException(SR.GetResourceString(SR.ID0422));
+        }
+
         return await registration.ConfigurationManager
             .GetConfigurationAsync(cancellationToken)
             .WaitAsync(cancellationToken) ??
@@ -207,6 +217,11 @@ public sealed class OpenIddictClientService
         }
 
         var registration = await GetClientRegistrationByIdAsync(identifier, cancellationToken);
+        if (registration.ConfigurationManager is null)
+        {
+            throw new InvalidOperationException(SR.GetResourceString(SR.ID0422));
+        }
+
         return await registration.ConfigurationManager
             .GetConfigurationAsync(cancellationToken)
             .WaitAsync(cancellationToken) ??