googl_shorten_url.php

<?php
/* Shorten a URL using Google's goo.gl API. Requires an API key. */
function googl_shorten_url($url, $api_key) {
  $endpoint = 'https://www.googleapis.com/urlshortener/v1';
  $ch = curl_init(sprintf('%s/url?key=%s', $endpoint, $api_key));
  curl_setopt_array($ch, array(
      \CURLOPT_POST           => true
    , \CURLOPT_AUTOREFERER    => true
    , \CURLOPT_FOLLOWLOCATION => true
    , \CURLOPT_SSL_VERIFYPEER => false
    , \CURLOPT_RETURNTRANSFER => true
    , \CURLOPT_HTTPHEADER     => array('Content-Type: application/json')
    , \CURLOPT_POSTFIELDS     => json_encode(array('longUrl' => $url)))
  );
  $res = curl_exec($ch);
  curl_close($ch);
  return json_decode($res, true);
}