public static function getCredential($userId)
    {
        $model = new User_Credential();
        $where = 'account_id = ' . $model->_toDb($userId, 'account_id');
        $creds = $model->getList(array(
            'filter' => $where
        ));
        if ($creds === false or count($creds) !== 1) {
            return false;
        }
        return $creds[0];
    }