Add HubMetdata (#8425)

- Added HubMetadata to detect the hub type on Endpoints
- Added a test

src/SignalR/server/Core/ref/Microsoft.AspNetCore.SignalR.Core.netcoreapp3.0.cs

@@ -183,6 +183,11 @@ namespace Microsoft.AspNetCore.SignalR
         public abstract System.Threading.Tasks.Task SendUserAsync(string userId, string methodName, object[] args, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken));
         public abstract System.Threading.Tasks.Task SendUsersAsync(System.Collections.Generic.IReadOnlyList<string> userIds, string methodName, object[] args, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken));
     }
+    public partial class HubMetadata
+    {
+        public HubMetadata(System.Type hubType) { }
+        public System.Type HubType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Method, AllowMultiple=false, Inherited=true)]
     public partial class HubMethodNameAttribute : System.Attribute
     {

src/SignalR/server/Core/src/HubMetadata.cs

@@ -0,0 +1,23 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.AspNetCore.SignalR
+{
+    /// <summary>
+    /// Metadata that describes the <see cref="Hub"/> information associated with a specific endpoint.
+    /// </summary>
+    public class HubMetadata
+    {
+        public HubMetadata(Type hubType)
+        {
+            HubType = hubType;
+        }
+
+        /// <summary>
+        /// The type of <see cref="Hub"/>.
+        /// </summary>
+        public Type HubType { get; }
+    }
+}

src/SignalR/server/SignalR/src/HubEndpointRouteBuilderExtensions.cs

@@ -67,6 +67,9 @@ namespace Microsoft.AspNetCore.Builder
                 {
                     e.Metadata.Add(item);
                 }
+
+                // Add metadata that captures the hub type this endpoint is associated with
+                e.Metadata.Add(new HubMetadata(typeof(THub)));
             });
 
             return conventionBuilder;

src/SignalR/server/SignalR/test/MapSignalRTests.cs

@@ -185,6 +185,27 @@ namespace Microsoft.AspNetCore.SignalR.Tests
             }
         }
 
+        [Fact]
+        public void MapHubEndPointRoutingAppliesHubMetadata()
+        {
+            void ConfigureRoutes(IEndpointRouteBuilder routes)
+            {
+                // This "Foo" policy should override the default auth attribute
+                routes.MapHub<AuthHub>("/path");
+            }
+
+            using (var host = BuildWebHostWithEndPointRouting(ConfigureRoutes))
+            {
+                host.Start();
+
+                var dataSource = host.Services.GetRequiredService<EndpointDataSource>();
+                // We register 2 endpoints (/negotiate and /)
+                Assert.Equal(2, dataSource.Endpoints.Count);
+                Assert.Equal(typeof(AuthHub), dataSource.Endpoints[0].Metadata.GetMetadata<HubMetadata>()?.HubType);
+                Assert.Equal(typeof(AuthHub), dataSource.Endpoints[1].Metadata.GetMetadata<HubMetadata>()?.HubType);
+            }
+        }
+
         private class InvalidHub : Hub
         {
             public void OverloadedMethod(int num)