title: Get Facebook User ID with Facebook App Scope ID
body: <p>Is it possible to get origin facebook id from facebook app scope id? </p>
  
  <p>I have 2 apps that shares the same database, so that user only need to sign up in one app in order to login both.
  This was working until facebook update their api from 1.0 to 2.0.
  Now, each user will have different fb scope id in each of them. I can't use fb id reference to the same user obj anymore.</p>