title: Prevent signups with Facebook proxy email
body: <p>Problem is, when a user clicks on FB Login button on my site, Facebook API throws him with a window which ask for access permissions(which is the usual flow). But when the user chooses the proxy mail address (anonymous), then I want to force the user to login only using his real email id.</p>
  
  <p>How am I supposed to handle this ?</p>
  
  <p>I can detect that user used proxy email and prevent him from registering, but then I can't remove my app from his list of authorized apps - meaning I can't get him to that initial dialog for choosing which email he will provide.</p>