code: func (s *Signer) Sign(req signer.SignRequest) (cert []byte, err error) {
  	resp, err := s.remoteOp(req, req.Profile, "sign")
  	if err != nil {
  		return
  	}
  	if cert, ok := resp.([]byte); ok {
  		return cert, nil
  	}
  	return
  }
docs: // Sign sends a signature request to the remote CFSSL server,
  // receiving a signed certificate or an error in response. The hostname,
  // csr, and profileName are used as with a local signing operation, and
  // the label is used to select a signing root in a multi-root CA.