title: how to get the access token from facebook ios sdk 3.1?
body: <p>how to get the access token from facebook ios sdk 3.1?</p>
  
  <p>I'm already getting the facebook login. Once the login is completed, the app comes to foreground. Although I could not yet figure out how to get the access token from this. </p>
  
  <p>I get null from [[FBSession activeSession] accessToken]; command.</p>
  
  <p>Any ideas? </p>