实施Google+一次性服务器流程

When trying to follow this example of implementing Google+ one-time-server-flow (hybrid): https://developers.google.com/+/web/signin/server-side-flow

I get the following error on my index page:

PHP Notice: Undefined variable: app in D:\home\site\wwwroot\beta\index.php on line 45 PHP Fatal error: Call to a member function set() on a non-object in D:\home\site\wwwroot\beta\index.php on line 45

    <?php
  require_once "includes/Google/Google_Client.php";
  require_once "includes/Google/contrib/Google_PlusService.php";

  // Create a state token to prevent request forgery.
  // Store it in the session for later validation.
  $state = md5(rand());
  $app['session']->set('state', $state);
  // Set the client ID, token state, and application name in the HTML while
  // serving it.
  return $app['twig']->render('index.php', array(
      'CLIENT_ID' => "ID HERE",
      'STATE' => $state,
      'APPLICATION_NAME' => "TEST APP"
  ));

?>

I have replace the CLIENT ID and APP NAME with examples for the purpose of posting on here.

Does anyone know what could be causing these errors? Thanks