yii\authclient\AuthAction::authOAuth2 PHP Method

    protected function authOAuth2($client)
    {
        if (isset($_GET['error'])) {
            if ($_GET['error'] == 'access_denied') {
                // user denied error
                return $this->redirectCancel();
            } else {
                // request error
                if (isset($_GET['error_description'])) {
                    $errorMessage = $_GET['error_description'];
                } elseif (isset($_GET['error_message'])) {
                    $errorMessage = $_GET['error_message'];
                } else {
                    $errorMessage = http_build_query($_GET);
                }
                throw new Exception('Auth error: ' . $errorMessage);
            }
        }
        // Get the access_token and save them to the session.
        if (isset($_GET['code'])) {
            $code = $_GET['code'];
            $token = $client->fetchAccessToken($code);
            if (!empty($token)) {
                return $this->authSuccess($client);
            } else {
                return $this->redirectCancel();
            }
        } else {
            $url = $client->buildAuthUrl();
            return Yii::$app->getResponse()->redirect($url);
        }
    }