function newUser($fullname, $credential, array $identifiers, array $meta = null)
    {
        $args = [
            'fullname'   => $fullname,
            'credential' => $credential,
            'meta'       => $meta,
        ] + $identifiers;

        $response = $this->call( new Command\Register($args) );
        if ( $ex = $response->hasException() )
            throw $ex;

        $r = $response->expected();
        $r = ($r instanceof iDataEntity) ? $r->get('result') : $r;
        return $r;
    }