Zend Auth example with extra columun

  $request = $this->getRequest();  
       if ($request->isPost()) {  
         $params = $this->filterInput($request->getParams());  
         $db = Zend_Db_Table_Abstract::getDefaultAdapter();  
         $auth = Zend_Auth::getInstance();  
         $authAdapter = new Zend_Auth_Adapter_DbTable($db, 'mdl_registration_user');  
         $authAdapter->setIdentityColumn('uname')  
             ->setCredentialColumn('password');  
         $authAdapter->setIdentity($params['uname'])  
             ->setCredential(md5($params['password']));  
         // extra validation  
         $authAdapter->getDbSelect()->where('countrycode = +'.$params['country']);  
         $result = $auth->authenticate($authAdapter);  
         if ($result->isValid()) {  
           $user = $authAdapter->getResultRowObject();  
           $auth->getStorage()->write($user);  
           $flash_obj->addMessage('You have loged-in successfully');  
           $this->_redirect('index/index');  
         } else {  
           $this->view->messages = "Invalid username or password. Please try again.";  
           return ;  
         }  
       }