Create a web service function that enrols users to a certain course

public static function enrol_users_parameters() {

        return new external_function_parameters(

            array(

                'enrolments' => new external_multiple_structure(

                    new external_single_structure(

                        array(

                            'roleid'    => new external_value(PARAM_INT, 'Role to assign to the user'),

                            'userid'    => new external_value(PARAM_INT, 'The user that is going to be enrolled'),

                            'contextid' => new external_value(PARAM_INT, 'The context to enrol the user role in'),

                        )

                    )

                )

            )

        );

    }

/**

     * Manual enrolment of users

     *

     * @param array $enrolments  An array of manual user enrolment

     * @return null

     */

    public static function enrol_users($enrolments) {

        global $DB, $USER;

        $params = self::validate_parameters(self::enrol_users_parameters(), array('enrolments'=>$enrolments));

        $transaction = $DB->start_delegated_transaction();

        foreach ($params['enrolments'] as $enrolment) {

            // Ensure the current user is allowed to run this function in the enrolment context

            $context = get_context_instance_by_id($enrolment['contextid']);

            self::validate_context($context);

            require_capability('moodle/role:assign', $context); //TODO: there is probably a capability related to enrolment, look for it and check on it it.

            $instance = $DB->get_record('enrol', array('courseid' => $context->instanceid, 'enrol' => 'manual'));

            $enrol = enrol_get_plugin('manual');

            $enrol->enrol_user($instance, $enrolment['userid'], $enrolment['roleid']);

            //TODO: maybe return a array of success/fail

        }

        $transaction->allow_commit();

    }

 /**

     * Returns description of method result value

     * @return external_description

     */

    public static function enrol_users_returns() {

        return null;

    }