PHP Zend Oauth and Google Docs

<?php
// set your path to Zend if you need it
$path = realpath('/home/piers/code/');
set_include_path($path . PATH_SEPARATOR . get_include_path());

require_once 'Zend/Oauth/Consumer.php';

session_start();

// set your Google consumer key / secret
$CONSUMER_KEY = 'your-consumer-key';
$CONSUMER_SECRET = 'your-consumer-secret';
$RETURN_TO = 'http://'.$_SERVER['HTTP_HOST'].$_SERVER['SCRIPT_NAME'];

// Multi-scoped token.
$SCOPES = array(
  'http://docs.google.com/feeds/',
);

$oauthOptions = array(
  'requestScheme' => Zend_Oauth::REQUEST_SCHEME_HEADER,
  'version' => '1.0',
  'consumerKey' => $CONSUMER_KEY,
  'consumerSecret' => $CONSUMER_SECRET,
  'signatureMethod' => 'HMAC-SHA1',
  'callbackUrl' => $RETURN_TO,
  'requestTokenUrl' => 'https://www.google.com/accounts/OAuthGetRequestToken',
  'userAuthorizationUrl' => 'https://www.google.com/accounts/OAuthAuthorizeToken',
  'accessTokenUrl' => 'https://www.google.com/accounts/OAuthGetAccessToken'
);

$consumer = new Zend_Oauth_Consumer($oauthOptions);

if (!isset($_SESSION['REQUEST_TOKEN'])) {
  $_SESSION['REQUEST_TOKEN'] = serialize($consumer->getRequestToken(array('scope' => implode(' ', $SCOPES))));
  $approvalUrl = $consumer->getRedirectUrl(array('hd' => 'default'));
  echo "<a href=\"$approvalUrl\">Grant access</a>";
  exit(0);
}

if (!isset($_SESSION['ACCESS_TOKEN'])) {
  if (!empty($_GET) && isset($_SESSION['REQUEST_TOKEN'])) {
    $_SESSION['ACCESS_TOKEN'] = serialize($consumer->getAccessToken($_GET, unserialize($_SESSION['REQUEST_TOKEN'])));
  }
}
$accessToken = unserialize($_SESSION['ACCESS_TOKEN']);
unset($_SESSION['REQUEST_TOKEN']);
unset($_SESSION['ACCESS_TOKEN']);

require_once 'Zend/Gdata/Docs.php';
$httpClient = $accessToken->getHttpClient($oauthOptions);
$client = new Zend_Gdata_Docs($httpClient, "yourCompany-YourAppName-v1");
$feed = $client->getDocumentListFeed();
echo "<pre>";
echo "<ul>\n";
foreach ($feed->entries as $entry) {
  echo "<li>$entry->title </li>\n";
}
echo "</ul>\n";
echo "</pre>\n";

exit(0);
?>