private function save($access_token, $time)
    {
        unset($this->runtime_file_content);

        $bytes = @file_put_contents($this->getFilePath(), json_encode(['a' => $access_token, 'e' => $time]));

        if ($bytes === false) {
            // fatal log will throw an exception
            $this->logger->fatal(__CLASS__, 'store', sprintf('Unable to store access token in %s', $this->getFilePath()));
        }

        $this->logger->debug(__CLASS__, 'store', sprintf('Access token stored in %s', $this->getFilePath()));

        return true;
    }