title: How to handle expired Facebook access tokens on iOS and FB SDK 3.7
body: <p>I'm using Facebook's iOS SDK 3.7 on my iOS app to handle logins. When I request post permissions it looks like the expiration date is about 2 months from the date of login.</p>
  
  <p>I understand I can check the expiration date using <code>[FBSession activeSession].accessTokenData.expirationDate</code> but what happens, and how do I handle the token when the token expires?</p>
  
  <p>Do I run <code>[FBSession openActiveSessionWithReadPermissions:allowLoginUI:completionHandler:];</code> again?</p>