public function checkFieldKey(ServerRequest $request, Response $response): Response
    {
        $queryParams = $request->getQueryParams();
        $fieldKey = $queryParams['key'];
        $table = 'tt_content';
        if (isset($queryParams['table'])) {
            $table = $queryParams['table'];
        }

        $objectManager = GeneralUtility::makeInstance(ObjectManager::class);
        $storageRepository = $objectManager->get(StorageRepository::class);

        // check if fieldKey is available for this table
        $isAvailable = true;
        if ($storageRepository->loadField($table, $fieldKey)) {
            $isAvailable = false;
        }

        return new JsonResponse(['isAvailable' => $isAvailable]);
    }