public function authenticate()
 {
     $userTable = new VC_DbTable_User();
     $userInfo = $userTable->findUserByUsernameOrEmail($this->username);
     if ($userInfo) {
         $identity = new stdClass();
         $identity->username = $userInfo->username;
         $identity->email = $userInfo->email;
         $identity->userId = $userInfo->id;
         $identity->role = $userInfo->role;
         $identity->fullname = $userInfo->fullname;
         return new Zend_Auth_Result(Zend_Auth_Result::SUCCESS, $identity, array());
     }
     return new Zend_Auth_Result(Zend_Auth_Result::FAILURE, $this->username);
 }