Web API Authentication in ASP.NET 5

I’ve been studying ASP.NET 5 for some time now and there is something I’m yet confused. To implement authentication in Web API 2 what I used to do was basically use the OWIN OAuth Authentication Server Middleware. It was simple to use, I could configure just what I needed and there wasn’t a bunch of stuff I needed to put on the app without need for it.

401 Client ‘Negotiate’, Server ‘Negotiate,NTLM’ When Calling WCF Server to Server

Ok, I’ve read every thread & question I can find with this error and surprisingly have not found a solution. I’m trying to require Windows authentication on my IIS hosted WCF service (.NET 4.0) which, until now, has been optional. I have had a Windows authentication enabled endpoint available on the server for a while with several remote applications successfully using it. I’m now trying to switch our web applications and other server apps that use the WCF service over to this secured endpoint by giving them the exact same client configuration as the working remote clients, but the server apps are receiving a 401 with the message: