public function addUser($groupName, $username)
    {
        $groupDn = $this->dn($groupName);

        $userDn = $this->adldap->user()->dn($username);

        if ($groupDn && $userDn) {
            $add['member'] = $userDn;

            return $this->connection->modAdd($groupDn, $add);
        }

        return false;
    }