code: func (a *LocalKeyAgent) defaultHostPromptFunc(host string, key ssh.PublicKey, writer io.Writer, reader io.Reader) error {
  	var err error
  
  	userAnswer := "no"
  	if !a.noHosts[host] {
  		fmt.Fprintf(writer, "The authenticity of host '%s' can't be established. "+
  			"Its public key is:\n%s\nAre you sure you want to continue (yes/no)? ",
  			host, ssh.MarshalAuthorizedKey(key))
  
  		userAnswer, err = bufio.NewReader(reader).ReadString('\n')
  		if err != nil {
  			return trace.Wrap(err)
  		}
  		userAnswer = strings.TrimSpace(strings.ToLower(userAnswer))
  	}
  	ok, err := utils.ParseBool(userAnswer)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	if !ok {
  		return trace.BadParameter("not trusted")
  	}
  	return nil
  }
docs: // defaultHostPromptFunc is the default host key/certificates prompt.