private function addRequiredParameters(array $parameters)
    {
        $parameters['AWSAccessKeyId'] = $this->awsAccessKeyId;
        $parameters['Timestamp'] = $this->getFormattedTimestamp(new DateTime('now', new DateTimeZone('UTC')));
        $parameters['Version'] = self::SERVICE_VERSION;
        $parameters['SignatureVersion'] = $this->config['SignatureVersion'];
        if ($parameters['SignatureVersion'] > 1) {
            $parameters['SignatureMethod'] = $this->config['SignatureMethod'];
        }
        $parameters['Signature'] = $this->signParameters($parameters, $this->awsSecretAccessKey);

        return $parameters;
    }