Facebook application: user identification

<?php
require_once '../common/facebook.php';
$appapikey = 'eff48960c4b2c6ede8096fd99eae2215';
$appsecret = '60dd4e4368ea026102e77c29bf4a721a';
$facebook = new Facebook($appapikey, $appsecret);
$user_id = $facebook->require_login();
include 'connection.php';  

?>

This code used to work, but since the API changes, this line seems to be the problem:

$user_id = $facebook->require_login();

If I delete it, the app runs, but doesn't recognize the Facebook user. So I think I need the correct syntax. Any suggestions will be very much appreciated.