aspnetcore_1/solution/solution.patch

diff --git a/src/Http/Http.Abstractions/src/Metadata/ApiEndpointMetadata.cs b/src/Http/Http.Abstractions/src/Metadata/ApiEndpointMetadata.cs
new file mode 100644
index 00000000..815bf2c8
--- /dev/null
+++ b/src/Http/Http.Abstractions/src/Metadata/ApiEndpointMetadata.cs
@@ -0,0 +1,20 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.AspNetCore.Http.Metadata;
+
+/// <summary>
+/// Metadata that indicates the endpoint is intended for API clients.
+/// When present, authentication handlers should prefer returning status codes over browser redirects.
+/// </summary>
+internal sealed class ApiEndpointMetadata : IApiEndpointMetadata
+{
+    /// <summary>
+    /// Singleton instance of <see cref="ApiEndpointMetadata"/>.
+    /// </summary>
+    public static readonly ApiEndpointMetadata Instance = new();
+
+    private ApiEndpointMetadata()
+    {
+    }
+}
diff --git a/src/Http/Http.Abstractions/src/Metadata/IApiEndpointMetadata.cs b/src/Http/Http.Abstractions/src/Metadata/IApiEndpointMetadata.cs
new file mode 100644
index 00000000..cadaafca
--- /dev/null
+++ b/src/Http/Http.Abstractions/src/Metadata/IApiEndpointMetadata.cs
@@ -0,0 +1,12 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.AspNetCore.Http.Metadata;
+
+/// <summary>
+/// Metadata that indicates the endpoint is an API intended for programmatic access rather than direct browser navigation.
+/// When present, authentication handlers should prefer returning status codes over browser redirects.
+/// </summary>
+public interface IApiEndpointMetadata
+{
+}
diff --git a/src/Http/Http.Abstractions/src/Microsoft.AspNetCore.Http.Abstractions.csproj b/src/Http/Http.Abstractions/src/Microsoft.AspNetCore.Http.Abstractions.csproj
index d383efa6..37e17a0f 100644
--- a/src/Http/Http.Abstractions/src/Microsoft.AspNetCore.Http.Abstractions.csproj
+++ b/src/Http/Http.Abstractions/src/Microsoft.AspNetCore.Http.Abstractions.csproj
@@ -35,7 +35,6 @@ Microsoft.AspNetCore.Http.HttpResponse</Description>
   </ItemGroup>
 
   <ItemGroup>
-    <InternalsVisibleTo Include="Microsoft.AspNetCore.Http.Abstractions.Microbenchmarks" />
     <InternalsVisibleTo Include="Microsoft.AspNetCore.Http.Extensions" />
     <InternalsVisibleTo Include="Microsoft.AspNetCore.Http.Results" />
   </ItemGroup>
@@ -61,5 +60,6 @@ Microsoft.AspNetCore.Http.HttpResponse</Description>
 
   <ItemGroup>
     <InternalsVisibleTo Include="Microsoft.AspNetCore.Http.Abstractions.Tests" />
+    <InternalsVisibleTo Include="Microsoft.AspNetCore.Http.Abstractions.Microbenchmarks" />
   </ItemGroup>
 </Project>
diff --git a/src/Http/Http.Abstractions/src/PublicAPI.Unshipped.txt b/src/Http/Http.Abstractions/src/PublicAPI.Unshipped.txt
index 3a246130..2944a853 100644
--- a/src/Http/Http.Abstractions/src/PublicAPI.Unshipped.txt
+++ b/src/Http/Http.Abstractions/src/PublicAPI.Unshipped.txt
@@ -1,4 +1,5 @@
 #nullable enable
+Microsoft.AspNetCore.Http.Metadata.IApiEndpointMetadata
 Microsoft.AspNetCore.Http.Metadata.IDisableValidationMetadata
 Microsoft.AspNetCore.Http.ProducesResponseTypeMetadata.Description.get -> string?
 Microsoft.AspNetCore.Http.ProducesResponseTypeMetadata.Description.set -> void
diff --git a/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/RequestDelegateGenerator.cs b/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/RequestDelegateGenerator.cs
index f4e2ad0e..f5e2abac 100644
--- a/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/RequestDelegateGenerator.cs
+++ b/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/RequestDelegateGenerator.cs
@@ -248,7 +248,12 @@ public sealed class RequestDelegateGenerator : IIncrementalGenerator
 
                 if (hasFormBody)
                 {
-                    codeWriter.WriteLine(RequestDelegateGeneratorSources.AntiforgeryMetadataType);
+                    codeWriter.WriteLine(RequestDelegateGeneratorSources.AntiforgeryMetadataClass);
+                }
+
+                if (hasJsonBody || hasResponseMetadata)
+                {
+                    codeWriter.WriteLine(RequestDelegateGeneratorSources.ApiEndpointMetadataClass);
                 }
 
                 if (hasFormBody || hasJsonBody || hasResponseMetadata)
diff --git a/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/RequestDelegateGeneratorSources.cs b/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/RequestDelegateGeneratorSources.cs
index d7c7a480..b626db27 100644
--- a/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/RequestDelegateGeneratorSources.cs
+++ b/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/RequestDelegateGeneratorSources.cs
@@ -479,19 +479,39 @@ internal static class RequestDelegateGeneratorSources
     }
 """;
 
-    public static string AntiforgeryMetadataType = """
-file sealed class AntiforgeryMetadata : IAntiforgeryMetadata
-{
-    public static readonly IAntiforgeryMetadata ValidationRequired = new AntiforgeryMetadata(true);
-
-    public AntiforgeryMetadata(bool requiresValidation)
+    public static string AntiforgeryMetadataClass = """
+    file sealed class AntiforgeryMetadata : IAntiforgeryMetadata
     {
-        RequiresValidation = requiresValidation;
+        public static readonly IAntiforgeryMetadata ValidationRequired = new AntiforgeryMetadata(true);
+
+        public AntiforgeryMetadata(bool requiresValidation)
+        {
+            RequiresValidation = requiresValidation;
+        }
+
+        public bool RequiresValidation { get; }
     }
+""";
 
-    public bool RequiresValidation { get; }
-}
+    public static string ApiEndpointMetadataClass = """
+    file sealed class ApiEndpointMetadata : IApiEndpointMetadata
+    {
+        public static readonly ApiEndpointMetadata Instance = new();
+
+        private ApiEndpointMetadata()
+        {
+        }
+
+        public static void AddApiEndpointMetadataIfMissing(EndpointBuilder builder)
+        {
+            if (!builder.Metadata.Any(m => m is IApiEndpointMetadata))
+            {
+                builder.Metadata.Add(Instance);
+            }
+        }
+    }
 """;
+
     public static string GetGeneratedRouteBuilderExtensionsSource(string endpoints, string helperMethods, string helperTypes, ImmutableHashSet<string> verbs) => $$"""
 {{SourceHeader}}
 
diff --git a/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/StaticRouteHandlerModel/StaticRouteHandlerModel.Emitter.cs b/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/StaticRouteHandlerModel/StaticRouteHandlerModel.Emitter.cs
index 83790d44..97fe2dc9 100644
--- a/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/StaticRouteHandlerModel/StaticRouteHandlerModel.Emitter.cs
+++ b/src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/StaticRouteHandlerModel/StaticRouteHandlerModel.Emitter.cs
@@ -205,7 +205,7 @@ internal static class StaticRouteHandlerModelEmitter
             return;
         }
 
-        if (!endpoint.Response.IsAwaitable && (response.HasNoResponse || response.IsIResult))
+        if (response.HasNoResponse || response.IsIResult)
         {
             return;
         }
@@ -215,13 +215,10 @@ internal static class StaticRouteHandlerModelEmitter
         {
             codeWriter.WriteLine($"options.EndpointBuilder.Metadata.Add(new ProducesResponseTypeMetadata(statusCode: StatusCodes.Status200OK, type: typeof(string), contentTypes: GeneratedMetadataConstants.PlaintextContentType));");
         }
-        else if (response.IsAwaitable && response.ResponseType == null)
-        {
-            codeWriter.WriteLine($"options.EndpointBuilder.Metadata.Add(new ProducesResponseTypeMetadata(statusCode: StatusCodes.Status200OK, type: typeof(void), contentTypes: GeneratedMetadataConstants.PlaintextContentType));");
-        }
         else if (response.ResponseType is { } responseType)
         {
             codeWriter.WriteLine($$"""options.EndpointBuilder.Metadata.Add(new ProducesResponseTypeMetadata(statusCode: StatusCodes.Status200OK, type: typeof({{responseType.ToDisplayString(EmitterConstants.DisplayFormatWithoutNullability)}}), contentTypes: GeneratedMetadataConstants.JsonContentType));""");
+            codeWriter.WriteLine("ApiEndpointMetadata.AddApiEndpointMetadataIfMissing(options.EndpointBuilder);");
         }
     }
 
@@ -339,13 +336,15 @@ internal static class StaticRouteHandlerModelEmitter
             codeWriter.WriteLine("if (!serviceProviderIsService.IsService(type))");
             codeWriter.StartBlock();
             codeWriter.WriteLine("options.EndpointBuilder.Metadata.Add(new AcceptsMetadata(type: type, isOptional: isOptional, contentTypes: GeneratedMetadataConstants.JsonContentType));");
+            codeWriter.WriteLine("options.EndpointBuilder.Metadata.Add(ApiEndpointMetadata.Instance);");
             codeWriter.WriteLine("break;");
             codeWriter.EndBlock();
             codeWriter.EndBlock();
         }
         else
         {
-            codeWriter.WriteLine($"options.EndpointBuilder.Metadata.Add(new AcceptsMetadata(contentTypes: GeneratedMetadataConstants.JsonContentType));");
+            codeWriter.WriteLine("options.EndpointBuilder.Metadata.Add(new AcceptsMetadata(contentTypes: GeneratedMetadataConstants.JsonContentType));");
+            codeWriter.WriteLine("options.EndpointBuilder.Metadata.Add(ApiEndpointMetadata.Instance);");
         }
     }
 
diff --git a/src/Http/Http.Extensions/src/RequestDelegateFactory.cs b/src/Http/Http.Extensions/src/RequestDelegateFactory.cs
index 19965ef1..aaebe417 100644
--- a/src/Http/Http.Extensions/src/RequestDelegateFactory.cs
+++ b/src/Http/Http.Extensions/src/RequestDelegateFactory.cs
@@ -401,7 +401,14 @@ public static partial class RequestDelegateFactory
                 InferAntiforgeryMetadata(factoryContext);
             }
 
-            PopulateBuiltInResponseTypeMetadata(methodInfo.ReturnType, factoryContext.EndpointBuilder);
+            // If this endpoint expects a JSON request body, we assume its an API endpoint not intended for browser navigation.
+            // When present, authentication handlers should prefer returning status codes over browser redirects.
+            if (factoryContext.JsonRequestBodyParameter is not null)
+            {
+                factoryContext.EndpointBuilder.Metadata.Add(ApiEndpointMetadata.Instance);
+            }
+
+            PopulateBuiltInResponseTypeMetadata(methodInfo.ReturnType, factoryContext);
 
             // Add metadata provided by the delegate return type and parameter types next, this will be more specific than inferred metadata from above
             EndpointMetadataPopulator.PopulateMetadata(methodInfo, factoryContext.EndpointBuilder, factoryContext.Parameters);
@@ -1023,37 +1030,40 @@ public static partial class RequestDelegateFactory
         return Expression.Block(localVariables, checkParamAndCallMethod);
     }
 
-    private static void PopulateBuiltInResponseTypeMetadata(Type returnType, EndpointBuilder builder)
+    private static void PopulateBuiltInResponseTypeMetadata(Type returnType, RequestDelegateFactoryContext factoryContext)
     {
         if (returnType.IsByRefLike)
         {
             throw GetUnsupportedReturnTypeException(returnType);
         }
 
-        var isAwaitable = false;
         if (CoercedAwaitableInfo.IsTypeAwaitable(returnType, out var coercedAwaitableInfo))
         {
             returnType = coercedAwaitableInfo.AwaitableInfo.ResultType;
-            isAwaitable = true;
         }
 
         // Skip void returns and IResults. IResults might implement IEndpointMetadataProvider but otherwise we don't know what it might do.
-        if (!isAwaitable && (returnType == typeof(void) || typeof(IResult).IsAssignableFrom(returnType)))
+        if (returnType == typeof(void) || typeof(IResult).IsAssignableFrom(returnType))
         {
             return;
         }
 
+        var builder = factoryContext.EndpointBuilder;
+
         if (returnType == typeof(string))
         {
             builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(type: typeof(string), statusCode: 200, PlaintextContentType));
         }
-        else if (returnType == typeof(void))
-        {
-            builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(returnType, statusCode: 200, PlaintextContentType));
-        }
         else
         {
             builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(returnType, statusCode: 200, DefaultAcceptsAndProducesContentType));
+
+            if (factoryContext.JsonRequestBodyParameter is null)
+            {
+                // Since this endpoint responds with JSON, we assume its an API endpoint not intended for browser navigation,
+                // but we don't want to bother adding this metadata twice if we've already inferred it based on the expected JSON request body.
+                builder.Metadata.Add(ApiEndpointMetadata.Instance);
+            }
         }
     }
 
diff --git a/src/Http/Http.Results/src/Accepted.cs b/src/Http/Http.Results/src/Accepted.cs
index 5dbc5698..d71fe907 100644
--- a/src/Http/Http.Results/src/Accepted.cs
+++ b/src/Http/Http.Results/src/Accepted.cs
@@ -82,5 +82,6 @@ public sealed class Accepted : IResult, IEndpointMetadataProvider, IStatusCodeHt
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status202Accepted, typeof(void)));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/AcceptedAtRoute.cs b/src/Http/Http.Results/src/AcceptedAtRoute.cs
index 74725595..900ee507 100644
--- a/src/Http/Http.Results/src/AcceptedAtRoute.cs
+++ b/src/Http/Http.Results/src/AcceptedAtRoute.cs
@@ -109,5 +109,6 @@ public sealed class AcceptedAtRoute : IResult, IEndpointMetadataProvider, IStatu
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status202Accepted, typeof(void)));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/AcceptedAtRouteOfT.cs b/src/Http/Http.Results/src/AcceptedAtRouteOfT.cs
index e9467dbe..b8e4304a 100644
--- a/src/Http/Http.Results/src/AcceptedAtRouteOfT.cs
+++ b/src/Http/Http.Results/src/AcceptedAtRouteOfT.cs
@@ -123,5 +123,6 @@ public sealed class AcceptedAtRoute<TValue> : IResult, IEndpointMetadataProvider
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status202Accepted, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/AcceptedOfT.cs b/src/Http/Http.Results/src/AcceptedOfT.cs
index 6777d354..34607071 100644
--- a/src/Http/Http.Results/src/AcceptedOfT.cs
+++ b/src/Http/Http.Results/src/AcceptedOfT.cs
@@ -101,5 +101,6 @@ public sealed class Accepted<TValue> : IResult, IEndpointMetadataProvider, IStat
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status202Accepted, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/BadRequest.cs b/src/Http/Http.Results/src/BadRequest.cs
index 9eef74aa..0356afed 100644
--- a/src/Http/Http.Results/src/BadRequest.cs
+++ b/src/Http/Http.Results/src/BadRequest.cs
@@ -52,5 +52,6 @@ public sealed class BadRequest : IResult, IEndpointMetadataProvider, IStatusCode
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status400BadRequest, typeof(void)));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/BadRequestOfT.cs b/src/Http/Http.Results/src/BadRequestOfT.cs
index 4b932786..b8fa5142 100644
--- a/src/Http/Http.Results/src/BadRequestOfT.cs
+++ b/src/Http/Http.Results/src/BadRequestOfT.cs
@@ -66,5 +66,6 @@ public sealed class BadRequest<TValue> : IResult, IEndpointMetadataProvider, ISt
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status400BadRequest, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/Conflict.cs b/src/Http/Http.Results/src/Conflict.cs
index da162ed5..f0067ba4 100644
--- a/src/Http/Http.Results/src/Conflict.cs
+++ b/src/Http/Http.Results/src/Conflict.cs
@@ -52,5 +52,6 @@ public sealed class Conflict : IResult, IEndpointMetadataProvider, IStatusCodeHt
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status409Conflict, typeof(void)));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/ConflictOfT.cs b/src/Http/Http.Results/src/ConflictOfT.cs
index bbfb3c6a..dda54d9d 100644
--- a/src/Http/Http.Results/src/ConflictOfT.cs
+++ b/src/Http/Http.Results/src/ConflictOfT.cs
@@ -66,5 +66,6 @@ public sealed class Conflict<TValue> : IResult, IEndpointMetadataProvider, IStat
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status409Conflict, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/Created.cs b/src/Http/Http.Results/src/Created.cs
index 7766d91a..19595562 100644
--- a/src/Http/Http.Results/src/Created.cs
+++ b/src/Http/Http.Results/src/Created.cs
@@ -82,5 +82,6 @@ public sealed class Created : IResult, IEndpointMetadataProvider, IStatusCodeHtt
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status201Created, typeof(void)));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/CreatedAtRoute.cs b/src/Http/Http.Results/src/CreatedAtRoute.cs
index 2fb70fa2..2ff79596 100644
--- a/src/Http/Http.Results/src/CreatedAtRoute.cs
+++ b/src/Http/Http.Results/src/CreatedAtRoute.cs
@@ -109,5 +109,6 @@ public sealed class CreatedAtRoute : IResult, IEndpointMetadataProvider, IStatus
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status201Created, typeof(void)));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/CreatedAtRouteOfT.cs b/src/Http/Http.Results/src/CreatedAtRouteOfT.cs
index d13d6154..a2868afd 100644
--- a/src/Http/Http.Results/src/CreatedAtRouteOfT.cs
+++ b/src/Http/Http.Results/src/CreatedAtRouteOfT.cs
@@ -126,5 +126,6 @@ public sealed class CreatedAtRoute<TValue> : IResult, IEndpointMetadataProvider,
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status201Created, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/CreatedOfT.cs b/src/Http/Http.Results/src/CreatedOfT.cs
index 58d0638b..a12e52b9 100644
--- a/src/Http/Http.Results/src/CreatedOfT.cs
+++ b/src/Http/Http.Results/src/CreatedOfT.cs
@@ -100,5 +100,6 @@ public sealed class Created<TValue> : IResult, IEndpointMetadataProvider, IStatu
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status201Created, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/InternalServerErrorOfT.cs b/src/Http/Http.Results/src/InternalServerErrorOfT.cs
index 36ec9fed..c726debf 100644
--- a/src/Http/Http.Results/src/InternalServerErrorOfT.cs
+++ b/src/Http/Http.Results/src/InternalServerErrorOfT.cs
@@ -66,5 +66,6 @@ public sealed class InternalServerError<TValue> : IResult, IEndpointMetadataProv
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status500InternalServerError, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/JsonHttpResultOfT.cs b/src/Http/Http.Results/src/JsonHttpResultOfT.cs
index 4841e675..fea23060 100644
--- a/src/Http/Http.Results/src/JsonHttpResultOfT.cs
+++ b/src/Http/Http.Results/src/JsonHttpResultOfT.cs
@@ -2,8 +2,11 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics.CodeAnalysis;
+using System.Reflection;
 using System.Text.Json;
 using System.Text.Json.Serialization.Metadata;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http.Metadata;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
@@ -13,7 +16,7 @@ namespace Microsoft.AspNetCore.Http.HttpResults;
 /// <summary>
 /// An action result which formats the given object as JSON.
 /// </summary>
-public sealed partial class JsonHttpResult<TValue> : IResult, IStatusCodeHttpResult, IValueHttpResult, IValueHttpResult<TValue>, IContentTypeHttpResult
+public sealed partial class JsonHttpResult<TValue> : IResult, IEndpointMetadataProvider, IStatusCodeHttpResult, IValueHttpResult, IValueHttpResult<TValue>, IContentTypeHttpResult
 {
     /// <summary>
     /// Initializes a new instance of the <see cref="Json"/> class with the values.
@@ -117,7 +120,7 @@ public sealed partial class JsonHttpResult<TValue> : IResult, IStatusCodeHttpRes
                     typedJsonTypeInfo,
                     contentType: ContentType);
             }
-            
+
             return httpContext.Response.WriteAsJsonAsync(
                 Value,
                 JsonTypeInfo,
@@ -131,4 +134,9 @@ public sealed partial class JsonHttpResult<TValue> : IResult, IStatusCodeHttpRes
             ContentType,
             JsonSerializerOptions);
     }
+
+    static void IEndpointMetadataProvider.PopulateMetadata(MethodInfo method, EndpointBuilder builder)
+    {
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
+    }
 }
diff --git a/src/Http/Http.Results/src/NoContent.cs b/src/Http/Http.Results/src/NoContent.cs
index 987a06fc..35ffb3c5 100644
--- a/src/Http/Http.Results/src/NoContent.cs
+++ b/src/Http/Http.Results/src/NoContent.cs
@@ -52,5 +52,6 @@ public class NoContent : IResult, IEndpointMetadataProvider, IStatusCodeHttpResu
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status204NoContent, typeof(void)));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/NotFoundOfT.cs b/src/Http/Http.Results/src/NotFoundOfT.cs
index ad9c3a10..d37a4ee9 100644
--- a/src/Http/Http.Results/src/NotFoundOfT.cs
+++ b/src/Http/Http.Results/src/NotFoundOfT.cs
@@ -65,5 +65,6 @@ public sealed class NotFound<TValue> : IResult, IEndpointMetadataProvider, IStat
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status404NotFound, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/Ok.cs b/src/Http/Http.Results/src/Ok.cs
index 0db060d4..837a0fa7 100644
--- a/src/Http/Http.Results/src/Ok.cs
+++ b/src/Http/Http.Results/src/Ok.cs
@@ -51,5 +51,6 @@ public sealed class Ok : IResult, IEndpointMetadataProvider, IStatusCodeHttpResu
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status200OK, typeof(void)));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/OkOfT.cs b/src/Http/Http.Results/src/OkOfT.cs
index 108674fd..7f19598e 100644
--- a/src/Http/Http.Results/src/OkOfT.cs
+++ b/src/Http/Http.Results/src/OkOfT.cs
@@ -65,5 +65,6 @@ public sealed class Ok<TValue> : IResult, IEndpointMetadataProvider, IStatusCode
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status200OK, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/ProblemHttpResult.cs b/src/Http/Http.Results/src/ProblemHttpResult.cs
index 4fe63c42..8ac29336 100644
--- a/src/Http/Http.Results/src/ProblemHttpResult.cs
+++ b/src/Http/Http.Results/src/ProblemHttpResult.cs
@@ -4,6 +4,9 @@
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
+using System.Reflection;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http.Metadata;
 
 namespace Microsoft.AspNetCore.Http.HttpResults;
 
@@ -11,7 +14,7 @@ namespace Microsoft.AspNetCore.Http.HttpResults;
 /// An <see cref="IResult"/> that on execution will write Problem Details
 /// HTTP API responses based on <see href="https://tools.ietf.org/html/rfc7807"/>
 /// </summary>
-public sealed class ProblemHttpResult : IResult, IStatusCodeHttpResult, IContentTypeHttpResult, IValueHttpResult, IValueHttpResult<ProblemDetails>
+public sealed class ProblemHttpResult : IResult, IEndpointMetadataProvider, IStatusCodeHttpResult, IContentTypeHttpResult, IValueHttpResult, IValueHttpResult<ProblemDetails>
 {
     /// <summary>
     /// Creates a new <see cref="ProblemHttpResult"/> instance with
@@ -69,4 +72,13 @@ public sealed class ProblemHttpResult : IResult, IStatusCodeHttpResult, IContent
                 ContentType);
         }
     }
+
+    /// <inheritdoc/>
+    static void IEndpointMetadataProvider.PopulateMetadata(MethodInfo method, EndpointBuilder builder)
+    {
+        ArgumentNullException.ThrowIfNull(method);
+        ArgumentNullException.ThrowIfNull(builder);
+
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
+    }
 }
diff --git a/src/Http/Http.Results/src/ServerSentEventsResult.cs b/src/Http/Http.Results/src/ServerSentEventsResult.cs
index 448b2076..a7951acd 100644
--- a/src/Http/Http.Results/src/ServerSentEventsResult.cs
+++ b/src/Http/Http.Results/src/ServerSentEventsResult.cs
@@ -105,5 +105,6 @@ public sealed class ServerSentEventsResult<T> : IResult, IEndpointMetadataProvid
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status200OK, typeof(SseItem<T>), contentTypes: ["text/event-stream"]));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/UnprocessableEntity.cs b/src/Http/Http.Results/src/UnprocessableEntity.cs
index eef96dc9..49d39827 100644
--- a/src/Http/Http.Results/src/UnprocessableEntity.cs
+++ b/src/Http/Http.Results/src/UnprocessableEntity.cs
@@ -52,5 +52,6 @@ public sealed class UnprocessableEntity : IResult, IEndpointMetadataProvider, IS
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(new ProducesResponseTypeMetadata(StatusCodes.Status422UnprocessableEntity, typeof(void)));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/UnprocessableEntityOfT.cs b/src/Http/Http.Results/src/UnprocessableEntityOfT.cs
index 475a0bc3..2d1ee494 100644
--- a/src/Http/Http.Results/src/UnprocessableEntityOfT.cs
+++ b/src/Http/Http.Results/src/UnprocessableEntityOfT.cs
@@ -66,5 +66,6 @@ public sealed class UnprocessableEntity<TValue> : IResult, IEndpointMetadataProv
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(TValue), StatusCodes.Status422UnprocessableEntity, ContentTypeConstants.ApplicationJsonContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Http/Http.Results/src/ValidationProblem.cs b/src/Http/Http.Results/src/ValidationProblem.cs
index ba738cfb..c4a539c9 100644
--- a/src/Http/Http.Results/src/ValidationProblem.cs
+++ b/src/Http/Http.Results/src/ValidationProblem.cs
@@ -77,5 +77,6 @@ public sealed class ValidationProblem : IResult, IEndpointMetadataProvider, ISta
         ArgumentNullException.ThrowIfNull(builder);
 
         builder.Metadata.Add(ProducesResponseTypeMetadata.CreateUnvalidated(typeof(HttpValidationProblemDetails), StatusCodes.Status400BadRequest, ContentTypeConstants.ProblemDetailsContentTypes));
+        builder.Metadata.Add(ApiEndpointMetadata.Instance);
     }
 }
diff --git a/src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs b/src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs
index 89d45efc..2f25045d 100644
--- a/src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs
+++ b/src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs
@@ -332,10 +332,9 @@ internal sealed class EndpointMetadataApiDescriptionProvider : IApiDescriptionPr
         var defaultErrorType = errorMetadata?.Type ?? typeof(void);
         var contentTypes = new MediaTypeCollection();
 
-        // If the return type is an IResult or an awaitable IResult, then we should treat it as a void return type
-        // since we can't infer anything without additional metadata.
-        if (typeof(IResult).IsAssignableFrom(responseType) ||
-            producesResponseMetadata.Any(metadata => typeof(IResult).IsAssignableFrom(metadata.Type)))
+        // If the return type is an IResult or wrapped in a Task or ValueTask, then we should treat it as a void return type
+        // since we can't infer anything without additional metadata or requiring unreferenced code.
+        if (IsTaskOrValueTask(responseType) || typeof(IResult).IsAssignableFrom(responseType))
         {
             responseType = typeof(void);
         }
@@ -427,6 +426,23 @@ internal sealed class EndpointMetadataApiDescriptionProvider : IApiDescriptionPr
             return apiResponseType == metadataType ||
                 metadataType?.IsAssignableFrom(apiResponseType) == true;
         }
+
+        static bool IsTaskOrValueTask(Type returnType)
+        {
+            // If this method did not need to be trim-safe, we would use CoercedAwaitableInfo.IsTypeAwaitable, but we cannot.
+            if (returnType.IsAssignableFrom(typeof(Task)) || returnType.IsAssignableFrom(typeof(ValueTask)))
+            {
+                return true;
+            }
+
+            if (returnType.FullName is null)
+            {
+                return false;
+            }
+
+            return returnType.FullName.StartsWith("System.Threading.Tasks.Task`1[", StringComparison.Ordinal) ||
+                returnType.FullName.StartsWith("System.Threading.Tasks.ValueTask`1[", StringComparison.Ordinal);
+        }
     }
 
     private static ApiResponseType CreateDefaultApiResponseType(Type responseType)
diff --git a/src/Mvc/Mvc.Core/src/ApiControllerAttribute.cs b/src/Mvc/Mvc.Core/src/ApiControllerAttribute.cs
index a1b95b3e..f7179b0b 100644
--- a/src/Mvc/Mvc.Core/src/ApiControllerAttribute.cs
+++ b/src/Mvc/Mvc.Core/src/ApiControllerAttribute.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using Microsoft.AspNetCore.Http.Metadata;
 using Microsoft.AspNetCore.Mvc.Infrastructure;
 
 namespace Microsoft.AspNetCore.Mvc;
@@ -17,6 +18,6 @@ namespace Microsoft.AspNetCore.Mvc;
 /// </para>
 /// </summary>
 [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
-public class ApiControllerAttribute : ControllerAttribute, IApiBehaviorMetadata
+public class ApiControllerAttribute : ControllerAttribute, IApiBehaviorMetadata, IApiEndpointMetadata
 {
 }
diff --git a/src/Security/Authentication/Cookies/src/CookieAuthenticationEvents.cs b/src/Security/Authentication/Cookies/src/CookieAuthenticationEvents.cs
index be47982a..994d999a 100644
--- a/src/Security/Authentication/Cookies/src/CookieAuthenticationEvents.cs
+++ b/src/Security/Authentication/Cookies/src/CookieAuthenticationEvents.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Metadata;
 using Microsoft.Net.Http.Headers;
 
 namespace Microsoft.AspNetCore.Authentication.Cookies;
@@ -41,7 +42,7 @@ public class CookieAuthenticationEvents
     /// </summary>
     public Func<RedirectContext<CookieAuthenticationOptions>, Task> OnRedirectToLogin { get; set; } = context =>
     {
-        if (IsAjaxRequest(context.Request))
+        if (IsAjaxRequest(context.Request) || IsApiEndpoint(context.HttpContext))
         {
             context.Response.Headers.Location = context.RedirectUri;
             context.Response.StatusCode = 401;
@@ -58,7 +59,7 @@ public class CookieAuthenticationEvents
     /// </summary>
     public Func<RedirectContext<CookieAuthenticationOptions>, Task> OnRedirectToAccessDenied { get; set; } = context =>
     {
-        if (IsAjaxRequest(context.Request))
+        if (IsAjaxRequest(context.Request) || IsApiEndpoint(context.HttpContext))
         {
             context.Response.Headers.Location = context.RedirectUri;
             context.Response.StatusCode = 403;
@@ -108,6 +109,12 @@ public class CookieAuthenticationEvents
             string.Equals(request.Headers.XRequestedWith, "XMLHttpRequest", StringComparison.Ordinal);
     }
 
+    private static bool IsApiEndpoint(HttpContext context)
+    {
+        var endpoint = context.GetEndpoint();
+        return endpoint?.Metadata.GetMetadata<IApiEndpointMetadata>() is not null;
+    }
+
     /// <summary>
     /// Invoked to validate the principal.
     /// </summary>
diff --git a/src/SignalR/common/Http.Connections/src/ConnectionEndpointRouteBuilderExtensions.cs b/src/SignalR/common/Http.Connections/src/ConnectionEndpointRouteBuilderExtensions.cs
index 8ed01395..f1aad864 100644
--- a/src/SignalR/common/Http.Connections/src/ConnectionEndpointRouteBuilderExtensions.cs
+++ b/src/SignalR/common/Http.Connections/src/ConnectionEndpointRouteBuilderExtensions.cs
@@ -5,6 +5,7 @@ using System.Diagnostics.CodeAnalysis;
 using Microsoft.AspNetCore.Connections;
 using Microsoft.AspNetCore.Http.Connections;
 using Microsoft.AspNetCore.Http.Connections.Internal;
+using Microsoft.AspNetCore.Http.Metadata;
 using Microsoft.AspNetCore.Http.Timeouts;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
@@ -125,6 +126,9 @@ public static class ConnectionEndpointRouteBuilderExtensions
             {
                 e.Metadata.Add(data);
             }
+
+            // Add IApiEndpointMetadata to indicate this is a non-browser endpoint (SignalR)
+            e.Metadata.Add(ApiEndpointMetadata.Instance);
         });
 
         return new ConnectionEndpointRouteBuilder(compositeConventionBuilder);
@@ -155,4 +159,9 @@ public static class ConnectionEndpointRouteBuilderExtensions
             }
         }
     }
+
+    private sealed class ApiEndpointMetadata : IApiEndpointMetadata
+    {
+        public static ApiEndpointMetadata Instance { get; } = new();
+    }
 }