protected function _getRegisterHelper() {
        $registerHelper = $this->_helper->getHelper('Register');
        if (!$registerHelper) {
            return null;
        }
        if (!$registerHelper instanceof Garp_Controller_Helper_Register) {
            throw new Garp_Auth_Exception(self::EXCEPTION_INVALID_REGISTER_HELPER);
        }
        return $registerHelper;
    }