title: OAuth - Binding local user to 3rd party
body: <p>I'm working on a mobile application, in which, the user can go for Facebook, Twitter or Foursquare authorization (via OAuth) rather than creating a new account and password. </p>
  
  <p>The problem is, I'm not sure what should I store in my DB to point a 3rd party account. The <code>auth_token</code>, acquired from OAuth process seems to expire or change in some situations (like when the user changes password). So, it's not a good option.</p>
  
  <p>What would be the long term option? I mean, even if user unauthorized my app, then authorizes it back, I would like to be able to find out the local user corresponding to them. Should I use the respective API's of each website and dig out <code>user_id</code> and store it? That would be consistent in between sessions I believe.</p>
  
  <p>Any suggestions?</p>
  
  <p>Thanks.</p>