Jose\Signer::computeSignature PHP Method

    private function computeSignature(Object\JWSInterface $jws, Object\SignatureInterface &$signature)
    {
        if (null === $signature->getSignatureKey()) {
            return;
        }
        $this->checkKeyUsage($signature->getSignatureKey(), 'signature');
        $signature_algorithm = $this->getSignatureAlgorithm($signature->getAllHeaders(), $signature->getSignatureKey());
        $input = $this->getInputToSign($jws, $signature);
        $value = $signature_algorithm->sign($signature->getSignatureKey(), $input);
        $signature = Object\Signature::createSignatureFromLoadedData($value, $signature->getEncodedProtectedHeaders(), $signature->getHeaders());
    }