public function actionDeregister($id)
    {
        $id = (int)$id;
        if (Yii::$app->user->identity->getID() == $id) {
            throw new ForbiddenHttpException(Yii::t('user', 'You cannot deregister yourself.'));
        }
        $user = $this->getUser($id);
        try {
            $result = $user->deregister();
            if ($result instanceof \Exception) {
                throw $result;
            }
        } catch (\Exception $ex) {
            throw new ServerErrorHttpException($ex->getMessage());
        }
        if ($result !== true) {
            throw new ServerErrorHttpException(Yii::t('user', 'Failed to deregister user.'));
        }
        Yii::$app->session->setFlash(Module::SESSION_KEY_RESULT, Module::RESULT_SUCCESS);
        Yii::$app->session->setFlash(Module::SESSION_KEY_MESSAGE, '(' . $user->getID() . ') ' . $this->deregisterSuccessMessage);
        return $this->redirect(['index']);
    }