code: public function actionConnect($account_id)
      {
          $account = $this->finder->findAccountById($account_id);
  
          if ($account === null || $account->getIsConnected()) {
              throw new NotFoundHttpException;
          }
  
          /** @var User $user */
          $user = \Yii::createObject([
              'class'    => User::className(),
              'scenario' => 'connect'
          ]);
  
          if ($user->load(\Yii::$app->request->post()) && $user->create()) {
              $account->user_id = $user->id;
              $account->save(false);
              \Yii::$app->user->login($user, $this->module->rememberFor);
              return $this->goBack();
          }
  
          return $this->render('connect', [
              'model'   => $user,
              'account' => $account
          ]);
      }
docs: Displays page where user can create new account that will be connected to social account.
  @param  integer $account_id
  @return string
  @throws NotFoundHttpException