Fix: SignalR Authorize & Firefox Compatibility

Changes in architecture to support authorization and temporary
workaround for NTLM in Firefox (to be removed in SignalR 2.x). Thanks to
@davidfowl

Disco.BI/BI/Interop/SignalRHandlers/SignalRAuthenticationWorkaround.cs

@@ -0,0 +1,58 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using System.Web;
+using System.Web.Routing;
+using System.Web.Security;
+using System.Web.SessionState;
+using Microsoft.AspNet.SignalR;
+using Owin;
+using AppFunc = System.Func<System.Collections.Generic.IDictionary<string, object>, System.Threading.Tasks.Task>;
+
+namespace Disco.BI.Interop.SignalRHandlers
+{
+    /// <summary>
+    /// Required for SignalR 1.1.0 NTLM support in Firefox & Safari
+    /// Returns 401 (Unauthorized) instead of 403 (Forbidden) when an unauthenticated request is processed
+    /// 
+    /// TODO: Remove this workaround when implementing SignalR 2.x
+    /// 
+    /// Thanks to David Fowler (@davidfowl)
+    /// </summary>
+    public static class SignalRAuthenticationWorkaround
+    {
+        public static void AddMiddleware(IAppBuilder app)
+        {
+            Func<AppFunc, AppFunc> convert403To401 = Convert403To401;
+
+            app.Use(convert403To401);
+        }
+
+        private static AppFunc Convert403To401(AppFunc next)
+        {
+            return env =>
+            {
+                // Execute the SignalR pipeline
+                Task task = next(env);
+
+                // Get the status code
+                int statusCode = 0;
+                if (env.ContainsKey("owin.ResponseStatusCode"))
+                {
+                    statusCode = (int)env["owin.ResponseStatusCode"];
+                }
+
+                // If its 403 then convert it to 401 (we shouldn't do 
+                // this if it's a cross domain request since it doesn't make sense)
+                if (statusCode == 403)
+                {
+                    env["owin.ResponseStatusCode"] = 401;
+                }
+
+                // Return the original task
+                return task;
+            };
+        }
+    }
+}