title: Get reference of facebook access token - Facebook SDK 4.X
body: <p>I have been using Facebook's login functionality to link to AWS Cognito system. To link them you require the <code>String</code> of Facebook's access token. Prior to version 4.0 I used </p>
  
  <pre><code>NSString *facebookToken = FBSession.activeSession.accessTokenData.accessToken;
  </code></pre>
  
  <p>Since the update this no longer works. I tried </p>
  
  <pre><code>NSString *facebookToken = FBSDKAccessTokenChangeNewKey;
  </code></pre>
  
  <p>But this also didn't work. Any suggestions? I can't find it in the reference guide or sample projects.</p>