Don't re-use DefaultHttpContext if IHttpContextAccessor is in use (#15049) (#20844)

* Don't re-use DefaultHttpContext if IHttpContextAccessor is in use
- Consumers may still get null or an ODE but will never end up with data from a different request.
- Make sure an ODE is thrown from all properties on HttpContext after the request is over.

Author: davidfowl

src/Hosting/Hosting/src/Http/DefaultHttpContextFactory.cs

@@ -26,6 +26,8 @@ public DefaultHttpContextFactory(IServiceProvider serviceProvider)
             _serviceScopeFactory = serviceProvider.GetRequiredService<IServiceScopeFactory>();
         }
 
+        internal IHttpContextAccessor HttpContextAccessor => _httpContextAccessor;
+
         public HttpContext Create(IFeatureCollection featureCollection)
         {
             if (featureCollection is null)

src/Hosting/Hosting/src/Internal/HostingApplication.cs

@@ -96,6 +96,14 @@ public void DisposeContext(Context context, Exception exception)
             if (_defaultHttpContextFactory != null)
             {
                 _defaultHttpContextFactory.Dispose((DefaultHttpContext)httpContext);
+
+                if (_defaultHttpContextFactory.HttpContextAccessor != null)
+                {
+                    // Clear the HttpContext if the accessor was used. It's likely that the lifetime extends
+                    // past the end of the http request and we want to avoid changing the reference from under
+                    // consumers.
+                    context.HttpContext = null;
+                }
             }
             else
             {