public static function add_cohort_member($username, $cohort_id)
 {
     global $CFG, $DB;
     $params = self::validate_parameters(self::add_cohort_member_parameters(), array('username' => $username, 'cohort_id' => $cohort_id));
     $auth = new auth_plugin_joomdle();
     $id = $auth->add_cohort_member($username, $cohort_id);
     return $id;
 }