$acceptable_domains = array("mycompany.com","myothercompany.net");

require_once 'google/appengine/api/users/UserService.php';
use googleappengineapiusersUserService;
$user = UserService::getCurrentUser();
$acceptable_domains = array("mycompany.com","myothercompany.net");

if(isset($user) && in_array(substr(strrchr($user->getEmail(), "@"),1),$acceptable_domains)){
 echo sprintf('<hr>Welcome, %s! (<a href="%s">sign out</a>)',
           $user->getNickname(),
           UserService::createLogoutUrl('/'));}
else {
 print 'user is not authorized to be here';
 echo sprintf('<a href="%s">Sign in or register</a>',UserService::createLoginUrl('/'));
}