/**
* /Admin/src/Admin/Module.php (e.g.)
*/
class Module
{
   public function onBootstrap(MvcEvent $e) {
     /* @var $sharedEventManager ZendEventManagerSharedEventManager */
     $sharedEventManager = $e->getApplication()->getEventManager()->getSharedManager();
     $sharedEventManager->attach(MvcEvent::EVENT_DISPATCH, array($this, 'doAuthentication'),1); // 1 is priority
   }

   /**
    * authentication processing
    */
   public function doAuthentication($event) {
      // your logic....
   }
}