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/AuthorizedPersistentConnection.cs

@@ -0,0 +1,36 @@
+using Microsoft.AspNet.SignalR;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Disco.BI.Interop.SignalRHandlers
+{
+    public class AuthorizedPersistentConnection : PersistentConnection
+    {
+        private string[] authorizedUserTypes = null;
+
+        protected virtual string[] AuthorizedUserTypes { get { return authorizedUserTypes; } }
+
+        protected override bool AuthorizeRequest(IRequest request)
+        {
+            if (!request.User.Identity.IsAuthenticated)
+                return false;
+            else
+            {
+                var user = UserBI.UserCache.CurrentUser;
+                if (user == null)
+                    return false;
+
+                if (AuthorizedUserTypes == null || AuthorizedUserTypes.Length == 0)
+                    return true;
+
+                if (AuthorizedUserTypes.Contains(user.Type))
+                    return true;
+
+                return false;
+            }
+        }
+    }
+}