title: IOS SDK Facebook SSO - User logs out from Facebook outside app?
body: <p>The instructions on using Single Sign-On (SSO) with the Facebook IOS SDK are to save the access token and expiration date in <code>fbDidLogin</code> and use them on subsequent calls to avoid unnecessary logins.</p>
  
  <p>But what if the user logs out of Facebook outside the app (e.g. in the Facebook app or in Safari)? The app doesn't know about this, so it tries to use the saved token and expiration date, and to my surprise - they are still valid and the app can access the user's data even though the user has logged out.</p>
  
  <p>Any way around this?</p>