Auth Identity

see this: http://framework.zend.com/manual/2.2/en/modules/zend.authentication.intro.html#usage

After successful login, how can I check in other pages whether a successful login is done?
It appears just this one is not working:

use Zend\Authentication\AuthenticationService;
$auth = new AuthenticationService();
if (!$auth->hasIdentity()) die();

how to check in other pages whether a login is already done?