MVC 5 Owin Facebook Auth results in Null Reference Exception

Question

I\'m trying to setup integrated OWIN Facebook authentication in a new MVC 5 project in Visual Studio 2013. I have configured apps and keys as per this tutorial:

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Answer 1

I started getting this in the latest VS 2013.3 template and realized the authentication wasn't playing nice with FormsAuthentication that I unnecessarily ported from one of my other projects. Here's what I did to fix it:

added ...

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