public function onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey)
    {
        // if the user hit a secure page and start() was called, this was
        // the URL they were on, and probably where you want to redirect to
        $targetPath = $request->getSession()->get('_security.'.$providerKey.'.target_path');

        if (!$targetPath) {
            $targetPath = $this->getDefaultSuccessRedirectUrl();
        }

        return new RedirectResponse($targetPath);
    }