Fix cross appdomain exception

Author: BrennanConroy

src/Microsoft.AspNetCore.Http/HttpContextAccessor.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 #if NET451
+using System;
 using System.Runtime.Remoting;
 using System.Runtime.Remoting.Messaging;
 #elif NETSTANDARD1_3
@@ -13,7 +14,7 @@ namespace Microsoft.AspNetCore.Http
     public class HttpContextAccessor : IHttpContextAccessor
     {
 #if NET451
-        private const string LogicalDataKey = "__HttpContext_Current__";
+        private static readonly string LogicalDataKey = "__HttpContext_Current__" + AppDomain.CurrentDomain.Id;
 
         public HttpContext HttpContext
         {

test/Microsoft.AspNetCore.Http.Tests/HttpContextFactoryTests.cs

@@ -1,6 +1,7 @@
 // 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;
 using Microsoft.AspNetCore.Http.Features;
 using Microsoft.Extensions.ObjectPool;
 using Microsoft.Extensions.Options;
@@ -34,5 +35,31 @@ public void AllowsCreatingContextWithoutSettingAccessor()
             var context = contextFactory.Create(new FeatureCollection());
             contextFactory.Dispose(context);
         }
+
+#if NET451
+        private static void DomainFunc()
+        {
+            var accessor = new HttpContextAccessor();
+            Assert.Equal(null, accessor.HttpContext);
+            accessor.HttpContext = new DefaultHttpContext();
+        }
+
+        [Fact]
+        public void ChangingAppDomainsDoesNotBreak()
+        {
+            // Arrange
+            var accessor = new HttpContextAccessor();
+            var contextFactory = new HttpContextFactory(new DefaultObjectPoolProvider(), Options.Create(new FormOptions()), accessor);
+            var domain = AppDomain.CreateDomain("newDomain");
+
+            // Act
+            var context = contextFactory.Create(new FeatureCollection());
+            domain.DoCallBack(DomainFunc);
+            AppDomain.Unload(domain);
+
+            // Assert
+            Assert.True(ReferenceEquals(context, accessor.HttpContext));
+        }
+#endif
     }
 }