yii\authclient\BaseOAuth::getAccessToken PHP Method

    public function getAccessToken()
    {
        if (!is_object($this->_accessToken)) {
            $this->_accessToken = $this->restoreAccessToken();
        }
        return $this->_accessToken;
    }

 /**
  *
  * @param BaseOAuth $client
  */
 public function successCallback($client)
 {
     $tokenParams = $client->getAccessToken()->getParams();
     $attributes = $client->getUserAttributes();
     if ($attributes['state'] == 'err') {
         throw new NotFoundHttpException($attributes['desc']);
     }
     $user = new User();
     $user->id = 'userdata';
     $user->userData = $attributes['customer'];
     $user->accessToken = $tokenParams['access_token'];
     $user->refreshToken = $tokenParams['refresh_token'];
     $user->authKey = time() . rand(10000, 99999);
     $user->save();
     Yii::$app->user->login($user, $tokenParams['expires_in']);
 }