code: func HostKeyPEM(bytes []byte) Option {
  	return func(srv *Server) error {
  		signer, err := gossh.ParsePrivateKey(bytes)
  		if err != nil {
  			return err
  		}
  
  		srv.AddHostKey(signer)
  
  		return nil
  	}
  }
docs: // HostKeyPEM returns a functional option that adds HostSigners to the server
  // from a PEM file as bytes.