title: OWIN's GetExternalLoginInfoAsync Always Returns null
body: <p>I've created a new MVC5 Web Application, and when I try to login with Google or Facebook, the <code>ExternalLoginCallback</code> Action in the <code>AccountController</code> is called, but <code>GetExternalLoginInfoAsync()</code> always returns null:</p>
  
  <pre><code>var loginInfo = await AuthenticationManager.GetExternalLoginInfoAsync();
  if (loginInfo == null)
  {
      return RedirectToAction("Login");
  }
  </code></pre>
  
  <p>Because it's always null, it just redirects back to the login page and the process starts over. How can I fix this?</p>