How to add a role on dektrium Yii2-user when creating?

Question

Yii

From the backend, when creating a new user, it is necessary that he be assigned the user role in the frontend, everything works, I can’t understand why it doesn’t work in the backend.
Here is the main.php part from the backend config

'modules' => [
        'user' => [
            // following line will restrict access to profile, recovery, registration and settings controllers from backend
           'as backend' => 'dektrium\user\filters\BackendFilter',
            'controllerMap' => [
                'admin' => 'backend\controllers\AdminController',
                'registration' => [
                    'class' => \backend\controllers\AdminController::className(),
                    'on ' . \backend\controllers\AdminController::EVENT_AFTER_CREATE  => function ($event) {

                        $auth = Yii::$app->authManager;
                        $role = $auth->getRole('user');
                        $user = \dektrium\user\models\User::findOne(['username' => $event->form->username]);
                        $auth->assign($role, $user->id);
                    }
                ],
            ],
        ],
        'user' => [
            'class'  => 'dektrium\user\Module',
            'admins' => ['admin'],
            'controllerMap' => [
                'admin' => 'backend\controllers\AdminController',
            ],

        ],

No action occurs.