Add interfaces for providing metadata from route handler types

- IProvideEndpointParameterMetadata
- IProvideEndpointResponseMetadata
- Contributes to #40646

Author: DamianEdwards

src/Http/Http.Extensions/src/IProvideEndpointParameterMetadata.cs

@@ -0,0 +1,22 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Reflection;
+
+namespace Microsoft.AspNetCore.Http;
+
+/// <summary>
+/// Indicates that a type provides a static method that returns <see cref="Endpoint"/> metadata when declared as the
+/// parameter type of a route handler delegate. The method must be of the form:
+/// <code>public static <see cref="IEnumerable{Object}"/> GetMetadata(<see cref="ParameterInfo"/> parameter, <see cref="IServiceProvider"/> services)</code>
+/// </summary>
+public interface IProvideEndpointParameterMetadata
+{
+    /// <summary>
+    /// Supplies objects to apply as metadata to the related <see cref="Endpoint"/>.
+    /// </summary>
+    /// <param name="parameter">The <see cref="ParameterInfo"/> that represents the parameter to the endpoint's route handler delegate.</param>
+    /// <param name="services">The application's <see cref="IServiceProvider"/>.</param>
+    /// <returns>The objects to apply as <see cref="Endpoint"/> metadata.</returns>
+    public static abstract IEnumerable<object> GetMetadata(ParameterInfo parameter, IServiceProvider services);
+}

src/Http/Http.Extensions/src/IProvideEndpointResponseMetadata.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;
+
+/// <summary>
+/// Indicates that a type provides a static method that returns <see cref="Endpoint"/> metadata when declared as the
+/// returned type of a <see cref="Endpoint"/> route handler delegate. The method must be of the form:
+/// <code>public static <see cref="IEnumerable{Object}"/> GetMetadata(<see cref="Endpoint"/> endpoint, <see cref="IServiceProvider"/> services)</code>
+/// </summary>
+public interface IProvideEndpointResponseMetadata
+{
+    /// <summary>
+    /// Supplies objects to apply as metadata to the related <see cref="Endpoint"/>.
+    /// </summary>
+    /// <param name="endpoint">The <see cref="Endpoint"/> the returned metadata will be applied to.</param>
+    /// <param name="services">The application's <see cref="IServiceProvider"/>.</param>
+    /// <returns>The objects to apply as <see cref="Endpoint"/> metadata.</returns>
+    public static abstract IEnumerable<object> GetMetadata(Endpoint endpoint, IServiceProvider services);
+}

src/Http/Http.Extensions/src/PublicAPI.Unshipped.txt

@@ -1,4 +1,8 @@
 #nullable enable
+Microsoft.AspNetCore.Http.IProvideEndpointParameterMetadata
+Microsoft.AspNetCore.Http.IProvideEndpointParameterMetadata.GetMetadata(System.Reflection.ParameterInfo! parameter, System.IServiceProvider! services) -> System.Collections.Generic.IEnumerable<object!>!
+Microsoft.AspNetCore.Http.IProvideEndpointResponseMetadata
+Microsoft.AspNetCore.Http.IProvideEndpointResponseMetadata.GetMetadata(Microsoft.AspNetCore.Http.Endpoint! endpoint, System.IServiceProvider! services) -> System.Collections.Generic.IEnumerable<object!>!
 Microsoft.AspNetCore.Http.RequestDelegateFactoryOptions.RouteHandlerFilterFactories.get -> System.Collections.Generic.IReadOnlyList<System.Func<Microsoft.AspNetCore.Http.RouteHandlerContext!, Microsoft.AspNetCore.Http.RouteHandlerFilterDelegate!, Microsoft.AspNetCore.Http.RouteHandlerFilterDelegate!>!>?
 Microsoft.AspNetCore.Http.RequestDelegateFactoryOptions.RouteHandlerFilterFactories.init -> void
 Microsoft.Extensions.DependencyInjection.RouteHandlerJsonServiceExtensions