private function signature($message)
    {
        return new Signature(
            $message,
            $this->key,
            $this->algorithm,
            $this->headerList
        );
    }
private function signature($message)
    {
        return new Signature(
            $message,
            $this->key,
            $this->algorithm,
            $this->headerList
        );
    }
@param RequestInterface $message

@return Signature