code: func (h finishedHash) selectClientCertSignatureAlgorithm(serverList []signatureAndHash, sigType uint8) (signatureAndHash, error) {
  	if h.version < VersionTLS12 {
  		// Nothing to negotiate before TLS 1.2.
  		return signatureAndHash{signature: sigType}, nil
  	}
  
  	for _, v := range serverList {
  		if v.signature == sigType && isSupportedSignatureAndHash(v, supportedSignatureAlgorithms) {
  			return v, nil
  		}
  	}
  	return signatureAndHash{}, errors.New("tls: no supported signature algorithm found for signing client certificate")
  }
docs: // selectClientCertSignatureAlgorithm returns a signatureAndHash to sign a
  // client's CertificateVerify with, or an error if none can be found.