I have the following code:

 $facebook = new Facebook(array(
                'appId'  => ID,
                'secret' => SECRET,
                'cookie' => true));


   $fb_uid = $facebook->getUser();


   if($fb_uid)
   {
   // check if person with fb_uid as facebook id in database, 
   // if so log them in. If not, register them.


    $fb_user = $facebook->api('/' . $fb_uid);


     I then get their email address using $fb_user['email'] and facebook_id and store in the database as a means to log them in the future

Sometimes $fb_uid returns false even though the person is logged in using facebook ... I think it is because the access token expires. how can I change this code to incorporate the extended access token to log in the user to my site?

offline access token is deprecated, so I need to use the extended access token.