diff --git a/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpBuilder.cs b/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpBuilder.cs
index 4b5e5929..8597c291 100644
--- a/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpBuilder.cs
+++ b/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpBuilder.cs
@@ -32,7 +32,7 @@ public sealed class OpenIddictClientSystemNetHttpBuilder
     public IServiceCollection Services { get; }
 
     /// <summary>
-    /// Amends the default OpenIddict client/server integration configuration.
+    /// Amends the default OpenIddict client/System.Net.Http configuration.
     /// </summary>
     /// <param name="configuration">The delegate used to configure the OpenIddict options.</param>
     /// <remarks>This extension can be safely called multiple times.</remarks>
@@ -49,6 +49,138 @@ public sealed class OpenIddictClientSystemNetHttpBuilder
         return this;
     }
 
+    /// <summary>
+    /// Configures the <see cref="HttpClient"/> used by the OpenIddict client/System.Net.Http integration.
+    /// </summary>
+    /// <remarks>
+    /// Note: customizations configured using this method apply to all providers.
+    /// </remarks>
+    /// <param name="configuration">The delegate used to configure the <see cref="HttpClient"/>.</param>
+    /// <returns>The <see cref="OpenIddictClientSystemNetHttpBuilder"/> instance.</returns>
+    [EditorBrowsable(EditorBrowsableState.Advanced)]
+    public OpenIddictClientSystemNetHttpBuilder ConfigureHttpClient(Action<HttpClient> configuration)
+    {
+        if (configuration is null)
+        {
+            throw new ArgumentNullException(nameof(configuration));
+        }
+
+        return Configure(options =>
+        {
+            if (options.HttpClientActions.TryGetValue(string.Empty, out var actions))
+            {
+                actions.Add(configuration);
+            }
+
+            else
+            {
+                options.HttpClientActions[string.Empty] = new(capacity: 1) { configuration };
+            }
+        });
+    }
+
+    /// <summary>
+    /// Configures the <see cref="HttpClient"/> used by the OpenIddict client/System.Net.Http integration.
+    /// </summary>
+    /// <remarks>
+    /// Note: customizations configured using this method only apply to the specified provider.
+    /// </remarks>
+    /// <param name="provider">The provider name, to which the customizations are applied.</param>
+    /// <param name="configuration">The delegate used to configure the <see cref="HttpClient"/>.</param>
+    /// <returns>The <see cref="OpenIddictClientSystemNetHttpBuilder"/> instance.</returns>
+    [EditorBrowsable(EditorBrowsableState.Advanced)]
+    public OpenIddictClientSystemNetHttpBuilder ConfigureHttpClient(string provider, Action<HttpClient> configuration)
+    {
+        if (string.IsNullOrEmpty(provider))
+        {
+            throw new ArgumentException(SR.FormatID0366(nameof(provider)), nameof(provider));
+        }
+
+        if (configuration is null)
+        {
+            throw new ArgumentNullException(nameof(configuration));
+        }
+
+        return Configure(options =>
+        {
+            if (options.HttpClientActions.TryGetValue(provider, out var actions))
+            {
+                actions.Add(configuration);
+            }
+
+            else
+            {
+                options.HttpClientActions[provider] = new(capacity: 1) { configuration };
+            }
+        });
+    }
+
+    /// <summary>
+    /// Configures the <see cref="HttpClientHandler"/> used by the OpenIddict client/System.Net.Http integration.
+    /// </summary>
+    /// <remarks>
+    /// Note: customizations configured using this method apply to all providers.
+    /// </remarks>
+    /// <param name="configuration">The delegate used to configure the <see cref="HttpClientHandler"/>.</param>
+    /// <returns>The <see cref="OpenIddictClientSystemNetHttpBuilder"/> instance.</returns>
+    [EditorBrowsable(EditorBrowsableState.Advanced)]
+    public OpenIddictClientSystemNetHttpBuilder ConfigureHttpClientHandler(Action<HttpClientHandler> configuration)
+    {
+        if (configuration is null)
+        {
+            throw new ArgumentNullException(nameof(configuration));
+        }
+
+        return Configure(options =>
+        {
+            if (options.HttpClientHandlerActions.TryGetValue(string.Empty, out var actions))
+            {
+                actions.Add(configuration);
+            }
+
+            else
+            {
+                options.HttpClientHandlerActions[string.Empty] = new(capacity: 1) { configuration };
+            }
+        });
+    }
+
+    /// <summary>
+    /// Configures the <see cref="HttpClientHandler"/> used by the OpenIddict client/System.Net.Http integration.
+    /// </summary>
+    /// <remarks>
+    /// Note: customizations configured using this method only apply to the specified provider.
+    /// </remarks>
+    /// <param name="provider">The provider name, to which the customizations are applied.</param>
+    /// <param name="configuration">The delegate used to configure the <see cref="HttpClientHandler"/>.</param>
+    /// <returns>The <see cref="OpenIddictClientSystemNetHttpBuilder"/> instance.</returns>
+    [EditorBrowsable(EditorBrowsableState.Advanced)]
+    public OpenIddictClientSystemNetHttpBuilder ConfigureHttpClientHandler(string provider, Action<HttpClientHandler> configuration)
+    {
+        if (string.IsNullOrEmpty(provider))
+        {
+            throw new ArgumentException(SR.FormatID0366(nameof(provider)), nameof(provider));
+        }
+
+        if (configuration is null)
+        {
+            throw new ArgumentNullException(nameof(configuration));
+        }
+
+        return Configure(options =>
+        {
+            if (options.HttpClientHandlerActions.TryGetValue(provider, out var actions))
+            {
+                actions.Add(configuration);
+            }
+
+            else
+            {
+                options.HttpClientHandlerActions[provider] = new(capacity: 1) { configuration };
+            }
+        });
+    }
+
     /// <summary>
     /// Sets the contact address used in the "From" header that is attached
     /// to the backchannel HTTP requests sent to the authorization server.
diff --git a/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpConfiguration.cs b/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpConfiguration.cs
index 2ca70f6b..036f3821 100644
--- a/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpConfiguration.cs
+++ b/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpConfiguration.cs
@@ -19,7 +19,6 @@ namespace OpenIddict.Client.SystemNetHttp;
 public sealed class OpenIddictClientSystemNetHttpConfiguration : IConfigureOptions<OpenIddictClientOptions>,
                                                                  IConfigureNamedOptions<HttpClientFactoryOptions>
 {
-#if !SUPPORTS_SERVICE_PROVIDER_IN_HTTP_MESSAGE_HANDLER_BUILDER
     private readonly IServiceProvider _provider;
 
     /// <summary>
@@ -28,7 +27,6 @@ public sealed class OpenIddictClientSystemNetHttpConfiguration : IConfigureOptio
     /// <param name="provider">The service provider.</param>
     public OpenIddictClientSystemNetHttpConfiguration(IServiceProvider provider)
         => _provider = provider ?? throw new ArgumentNullException(nameof(provider));
-#endif
 
     /// <inheritdoc/>
     public void Configure(OpenIddictClientOptions options)
@@ -60,15 +58,26 @@ public sealed class OpenIddictClientSystemNetHttpConfiguration : IConfigureOptio
             return;
         }
 
-        options.HttpClientActions.Add(options =>
+        var settings = _provider.GetRequiredService<IOptionsMonitor<OpenIddictClientSystemNetHttpOptions>>().CurrentValue;
+
+        options.HttpClientActions.Add(client =>
         {
             // By default, HttpClient uses a default timeout of 100 seconds and allows payloads of up to 2GB.
             // To help reduce the effects of malicious responses (e.g responses returned at a very slow pace
             // or containing an infine amount of data), the default values are amended to use lower values.
-            options.MaxResponseContentBufferSize = 10 * 1024 * 1024;
-            options.Timeout = TimeSpan.FromMinutes(1);
+            client.MaxResponseContentBufferSize = 10 * 1024 * 1024;
+            client.Timeout = TimeSpan.FromMinutes(1);
         });
 
+        // Register the user-defined HTTP client actions.
+        foreach (var action in settings.HttpClientActions
+            .Where(action => string.IsNullOrEmpty(action.Key) || // Note: actions that have an empty key apply to all providers.
+                             action.Key.AsSpan().Equals(name.AsSpan(assembly.Name!.Length + 1), StringComparison.Ordinal))
+            .SelectMany(action => action.Value))
+        {
+            options.HttpClientActions.Add(action);
+        }
+
         options.HttpMessageHandlerBuilderActions.Add(builder =>
         {
 #if SUPPORTS_SERVICE_PROVIDER_IN_HTTP_MESSAGE_HANDLER_BUILDER
@@ -98,5 +107,15 @@ public sealed class OpenIddictClientSystemNetHttpConfiguration : IConfigureOptio
                 builder.AdditionalHandlers.Add(new PolicyHttpMessageHandler(policy));
             }
         });
+
+        // Register the user-defined HTTP client handler actions.
+        foreach (var action in settings.HttpClientHandlerActions
+            .Where(action => string.IsNullOrEmpty(action.Key) || // Note: actions that have an empty key apply to all providers.
+                             action.Key.AsSpan().Equals(name.AsSpan(assembly.Name!.Length + 1), StringComparison.Ordinal))
+            .SelectMany(action => action.Value))
+        {
+            options.HttpMessageHandlerBuilderActions.Add(builder => action(builder.PrimaryHandler as HttpClientHandler ??
+                throw new InvalidOperationException(SR.FormatID0373(typeof(HttpClientHandler).FullName))));
+        }
     }
 }
diff --git a/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpOptions.cs b/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpOptions.cs
index 9a0d7d1f..d393314c 100644
--- a/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpOptions.cs
+++ b/src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpOptions.cs
@@ -36,4 +36,16 @@ public sealed class OpenIddictClientSystemNetHttpOptions
     /// attached to the backchannel HTTP requests sent to the authorization server.
     /// </summary>
     public ProductInfoHeaderValue? ProductInformation { get; set; }
+
+    /// <summary>
+    /// Gets the user-defined actions used to amend the <see cref="HttpClient"/>
+    /// instances created by the OpenIddict client/System.Net.Http integration.
+    /// </summary>
+    public Dictionary<string, List<Action<HttpClient>>> HttpClientActions { get; } = new();
+
+    /// <summary>
+    /// Gets the user-defined actions used to amend the <see cref="HttpClientHandler"/>
+    /// instances created by the OpenIddict client/System.Net.Http integration.
+    /// </summary>
+    public Dictionary<string, List<Action<HttpClientHandler>>> HttpClientHandlerActions { get; } = new();
 }
diff --git a/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpBuilder.cs b/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpBuilder.cs
index 209c2e88..d6a88253 100644
--- a/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpBuilder.cs
+++ b/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpBuilder.cs
@@ -32,7 +32,7 @@ public sealed class OpenIddictValidationSystemNetHttpBuilder
     public IServiceCollection Services { get; }
 
     /// <summary>
-    /// Amends the default OpenIddict validation/server integration configuration.
+    /// Amends the default OpenIddict validation/System.Net.Http configuration.
     /// </summary>
     /// <param name="configuration">The delegate used to configure the OpenIddict options.</param>
     /// <remarks>This extension can be safely called multiple times.</remarks>
@@ -49,6 +49,38 @@ public sealed class OpenIddictValidationSystemNetHttpBuilder
         return this;
     }
 
+    /// <summary>
+    /// Configures the <see cref="HttpClient"/> used by the OpenIddict validation/System.Net.Http integration.
+    /// </summary>
+    /// <param name="configuration">The delegate used to configure the <see cref="HttpClient"/>.</param>
+    /// <returns>The <see cref="OpenIddictValidationSystemNetHttpBuilder"/> instance.</returns>
+    [EditorBrowsable(EditorBrowsableState.Advanced)]
+    public OpenIddictValidationSystemNetHttpBuilder ConfigureHttpClient(Action<HttpClient> configuration)
+    {
+        if (configuration is null)
+        {
+            throw new ArgumentNullException(nameof(configuration));
+        }
+
+        return Configure(options => options.HttpClientActions.Add(configuration));
+    }
+
+    /// <summary>
+    /// Configures the <see cref="HttpClientHandler"/> used by the OpenIddict client/System.Net.Http integration.
+    /// </summary>
+    /// <param name="configuration">The delegate used to configure the <see cref="HttpClientHandler"/>.</param>
+    /// <returns>The <see cref="OpenIddictValidationSystemNetHttpBuilder"/> instance.</returns>
+    [EditorBrowsable(EditorBrowsableState.Advanced)]
+    public OpenIddictValidationSystemNetHttpBuilder ConfigureHttpClientHandler(Action<HttpClientHandler> configuration)
+    {
+        if (configuration is null)
+        {
+            throw new ArgumentNullException(nameof(configuration));
+        }
+
+        return Configure(options => options.HttpClientHandlerActions.Add(configuration));
+    }
+
     /// <summary>
     /// Sets the contact address used in the "From" header that is attached
     /// to the backchannel HTTP requests sent to the authorization server.
diff --git a/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpConfiguration.cs b/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpConfiguration.cs
index 9ec617f4..139ee8d2 100644
--- a/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpConfiguration.cs
+++ b/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpConfiguration.cs
@@ -19,7 +19,6 @@ namespace OpenIddict.Validation.SystemNetHttp;
 public sealed class OpenIddictValidationSystemNetHttpConfiguration : IConfigureOptions<OpenIddictValidationOptions>,
                                                                      IConfigureNamedOptions<HttpClientFactoryOptions>
 {
-#if !SUPPORTS_SERVICE_PROVIDER_IN_HTTP_MESSAGE_HANDLER_BUILDER
     private readonly IServiceProvider _provider;
     
     /// <summary>
@@ -28,7 +27,6 @@ public sealed class OpenIddictValidationSystemNetHttpConfiguration : IConfigureO
     /// <param name="provider">The service provider.</param>
     public OpenIddictValidationSystemNetHttpConfiguration(IServiceProvider provider)
         => _provider = provider ?? throw new ArgumentNullException(nameof(provider));
-#endif
 
     /// <inheritdoc/>
     public void Configure(OpenIddictValidationOptions options)
@@ -60,15 +58,23 @@ public sealed class OpenIddictValidationSystemNetHttpConfiguration : IConfigureO
             return;
         }
 
-        options.HttpClientActions.Add(options =>
+        var settings = _provider.GetRequiredService<IOptionsMonitor<OpenIddictValidationSystemNetHttpOptions>>().CurrentValue;
+
+        options.HttpClientActions.Add(client =>
         {
             // By default, HttpClient uses a default timeout of 100 seconds and allows payloads of up to 2GB.
             // To help reduce the effects of malicious responses (e.g responses returned at a very slow pace
             // or containing an infine amount of data), the default values are amended to use lower values.
-            options.MaxResponseContentBufferSize = 10 * 1024 * 1024;
-            options.Timeout = TimeSpan.FromMinutes(1);
+            client.MaxResponseContentBufferSize = 10 * 1024 * 1024;
+            client.Timeout = TimeSpan.FromMinutes(1);
         });
 
+        // Register the user-defined HTTP client actions.
+        foreach (var action in settings.HttpClientActions)
+        {
+            options.HttpClientActions.Add(action);
+        }
+
         options.HttpMessageHandlerBuilderActions.Add(builder =>
         {
 #if SUPPORTS_SERVICE_PROVIDER_IN_HTTP_MESSAGE_HANDLER_BUILDER
@@ -98,5 +104,12 @@ public sealed class OpenIddictValidationSystemNetHttpConfiguration : IConfigureO
                 builder.AdditionalHandlers.Add(new PolicyHttpMessageHandler(policy));
             }
         });
+
+        // Register the user-defined HTTP client handler actions.
+        foreach (var action in settings.HttpClientHandlerActions)
+        {
+            options.HttpMessageHandlerBuilderActions.Add(builder => action(builder.PrimaryHandler as HttpClientHandler ??
+                throw new InvalidOperationException(SR.FormatID0373(typeof(HttpClientHandler).FullName))));
+        }
     }
 }
diff --git a/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpOptions.cs b/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpOptions.cs
index d50946c6..a03ed869 100644
--- a/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpOptions.cs
+++ b/src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpOptions.cs
@@ -36,4 +36,16 @@ public sealed class OpenIddictValidationSystemNetHttpOptions
     /// attached to the backchannel HTTP requests sent to the authorization server.
     /// </summary>
     public ProductInfoHeaderValue? ProductInformation { get; set; }
+
+    /// <summary>
+    /// Gets the user-defined actions used to amend the <see cref="HttpClient"/>
+    /// instances created by the OpenIddict validation/System.Net.Http integration.
+    /// </summary>
+    public List<Action<HttpClient>> HttpClientActions { get; } = new();
+
+    /// <summary>
+    /// Gets the user-defined actions used to amend the <see cref="HttpClientHandler"/>
+    /// instances created by the OpenIddict validation/System.Net.Http integration.
+    /// </summary>
+    public List<Action<HttpClientHandler>> HttpClientHandlerActions { get; } = new();
 }