<?php

require './facebook.php';

$facebook = new Facebook(array(
  'appId'  => 'YOUR APP ID',
  'secret' => 'YOUR API SECRET',
  'cookie' => true, // enable optional cookie support
));

if ($facebook->getSession()) {
  echo '<a href="' . $facebook->getLogoutUrl() . '">Logout</a>';
} else {
  echo '<a href="' . $facebook->getLoginUrl() . '">Login</a>';
}