title: Why does my site redirect back to the Login screen when I click an external provider button?
body: <p>I'm upgrading an ASP.Net MVC4 site to MVC5, and implementing the new OWIN Authentication methods in the process.</p>
  
  <p>I've copied over the action methods from the Account controller on a blank MVC5 project.</p>
  
  <p>The problem is, when I click an external provider button (e.g. Google) I just get redirected back to the login page again. The second time I click it, I do get taken to the Google account page, but then the browser gets redirected to the Account/External login page.</p>
  
  <p>What's going on?</p>