public function isAuthorizedByUser( $scope, $user = null )
    {
        if ( $user === null )
            $user = eZUser::currentUser();

        if ( !$user->isRegistered() )
            throw new Exception( "Anonymous user can not authorize an application" );

        $authorized = ezpRestAuthorizedClient::fetchForClientUser( $this, $user );
        return ( $authorized instanceof ezpRestAuthorizedClient );
    }