src/Signer.php
private function signatureParameters($message)
    {
        return new SignatureParameters(
            $this->key,
            $this->algorithm,
            $this->headerList,
            $this->signature($message)
        );
    }
private function signatureParameters($message)
    {
        return new SignatureParameters(
            $this->key,
            $this->algorithm,
            $this->headerList,
            $this->signature($message)
        );
    }
@param RequestInterface $message

@return SignatureParameters