AuthSub using PHP's libcurl

<?
$secure = 0;
$session = 1;
$scope = 'http://www.google.com/calendar/feeds';
$next = "http://{$_SERVER['HTTP_HOST']}{$_SERVER['PHP_SELF']}";

$token = @$_GET['token'];  // only a single use token

if(!$token) {
 echo "<a href=\"https://www.google.com/accounts/AuthSubRequest?scope=$scope&session=$session&secure=$secure&next=$next\">Sign in to Google</a>";
 exit;
}

$sessionToken = upgradeToken($token);
echo "Single use token: $token\n";
echo "Session token: $sessionToken";

// TODO: get a feed

function upgradeToken($token) {
  $ch = curl_init("https://www.google.com/accounts/AuthSubSessionToken");
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
  curl_setopt($ch, CURLOPT_FAILONERROR, true);
  curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
  curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Authorization: AuthSub token="' . trim($token) . '"'
  ));

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

  $splitStr = split("=", $result);

  return trim($splitStr[1]);
}
?>