title: Get Access Token after Facebook login
body: <p>I need to implement Facebook login in my iOS app.</p>
  
  <p>I use latest sdk version and I try to get access token after login but every time I try to return it I get <code>null</code>.</p>
  
  <p>I follow all step of documentation but it still doesn't work and get <code>null</code> on access token return.</p>