Url Shortening with Goo.gl

gistfile1.php

<?php 
$longUrl = 'http://facebook.com';
$ch = curl_init();
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_URL, 'http://goo.gl/api/shorten');
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, 'security_token=null&url='.$longUrl);

$content = curl_exec($ch);
curl_close($ch);

echo json_encode($content);
?>