package main

import (
	"crypto/rand"
	"crypto/rsa"
	"log"
	"net"
	"os"
	"strings"

	"golang.org/x/crypto/ssh"
)

func main() {
	exit := func(v interface{}) {
		l := log.New(os.Stderr, "", 0)
		l.Printf("%v\n", v)
		os.Exit(-1)
	}

	args := os.Args[1:]
	if len(args) != 1 {
		exit("missing destination")
	}
	idx := strings.LastIndex(args[0], "@")
	if idx == -1 {
		exit("destination does not contain username")
	}
	user := args[0][:idx]
	dst := args[0][idx+1:]
	host, port, err := net.SplitHostPort(dst)
	if err != nil || port == "" {
		host = dst
		port = "22"
	}
	dst = net.JoinHostPort(host, port)

	key, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		exit(err)
	}

	signer, err := ssh.NewSignerFromKey(key)
	if err != nil {
		exit(err)
	}

	cfg := &ssh.ClientConfig{
		User: user,
		Auth: []ssh.AuthMethod{
			//ssh.PublicKeys(signer),
			ssh.PublicKeysCallback(func() ([]ssh.Signer, error) {
				log.Printf("PublicKeysCallback()")
				return []ssh.Signer{signer}, nil
			}),
			ssh.PasswordCallback(func() (secret string, err error) {
				log.Printf("PasswordCallback()")
				return "notaverysecretpassword", nil
			}),
			ssh.KeyboardInteractive(func(name, instruction string, questions []string, echos []bool) ([]string, error) {
				log.Printf("KeyboardInteractive()")
				return []string{"notaverysecretpassword"}, nil
			}),
		},
		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
	}

	log.Printf("connecting to %s@%s", user, dst)
	conn, err := ssh.Dial("tcp", dst, cfg)
	if err != nil {
		exit(err)
	}
	conn.Close()
}

$ ./sshclient root@192.168.200.105
2024/04/23 14:12:58 connecting to root@192.168.200.105:22
2024/04/23 14:12:58 PublicKeysCallback()
2024/04/23 14:12:58 PasswordCallback()
ssh: handshake failed: ssh: disconnect, reason 2: Too many authentication failures

$ ./sshclient root@192.168.200.105
2024/04/23 14:13:49 connecting to root@192.168.200.105:22
2024/04/23 14:13:49 PublicKeysCallback()
ssh: handshake failed: ssh: disconnect, reason 2: Too many authentication failures