public static function save_user_extensions_parameters() {
        return new external_function_parameters(
            array(
                'assignmentid' => new external_value(PARAM_INT, 'The assignment id to operate on'),
                'userids' => new external_multiple_structure(
                    new external_value(PARAM_INT, 'user id'),
                    '1 or more user ids',
                    VALUE_REQUIRED),
                'dates' => new external_multiple_structure(
                    new external_value(PARAM_INT, 'dates'),
                    '1 or more extension dates (timestamp)',
                    VALUE_REQUIRED),
            )
        );
    }