public function formExtendFields($form)
    {
        if ($form->getContext() == 'myaccount') {
            return;
        }

        if (!$this->user->isSuperUser()) {
            $form->removeField('is_superuser');
        }

        /*
         * Add permissions tab
         */
        $form->addTabFields($this->generatePermissionsField());

        /*
         * Mark default groups
         */
        if (!$form->model->exists) {
            $defaultGroupIds = UserGroup::where('is_new_user_default', true)->lists('id');

            $groupField = $form->getField('groups');
            $groupField->value = $defaultGroupIds;
        }
    }