Go - SSH Through Bastion Host

ssh_through_bastion_host.go

// I created this to attach to https://stackoverflow.com/questions/60046598/ssh-through-bastion-host
package main


import (
	"flag"
	"fmt"
	"golang.org/x/crypto/ssh"
	"golang.org/x/crypto/ssh/agent"
	"log"
	"net"
	"os"
	"os/user"
)

const TCP  = "tcp"
const PORT = "22"
const SOCKET = "SSH_AUTH_SOCK"
const UNIX = "unix"
func sshAgentConnect() agent.ExtendedAgent {
	socket := os.Getenv(SOCKET)
	conn, err := net.Dial(UNIX, socket)
	if err != nil {
		log.Fatalf("Failed to connect to %v", SOCKET)
	}
	agentClient := agent.NewClient(conn)
	return agentClient
}

func clientAuth(usr string, auth ssh.AuthMethod) *ssh.ClientConfig {
	config := &ssh.ClientConfig{
		User: usr,
		Auth: []ssh.AuthMethod{
			auth,
		},
		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
	}
	return config
}

func formatHost(host string) string {
	return fmt.Sprintf("%s:%s", host, PORT)
}
func main() {
	var usr, _ = user.Current()
	userF := flag.String("user", usr.Username, "user to connect as")
	bastionF := flag.String("bastion", "" , "Bation host to connect to")
	lanHostF := flag.String("host", "", "Lan Host to connect to")
	flag.Parse()
	var sshAgent = sshAgentConnect()
	var config = clientAuth(*userF, ssh.PublicKeysCallback(sshAgent.Signers))


	sshc, err := ssh.Dial(TCP, formatHost(*bastionF), config)
	if err != nil {
		log.Fatalf("Failed to connect to %s\n%v\n", *bastionF, err)
	}
	defer sshc.Close()

	lanConn, err := sshc.Dial(TCP, formatHost(*lanHostF))
	if err != nil {
		fmt.Printf("got error trying to dial %v\n -- %v\n", *lanHostF, err)
		log.Fatal(err)
	}
	defer lanConn.Close()

	ncc, chans, reqs, err := ssh.NewClientConn(lanConn, formatHost(*lanHostF), config)
	if err != nil {
		fmt.Printf("got error trying to get new client connection %v\n -- %v\n", formatHost(*lanHostF), err)
		log.Fatal(err)
	}

	sClient := ssh.NewClient(ncc, chans, reqs)

	defer sClient.Close()
	fmt.Printf("Connection to %v created at %v", *lanHostF, sClient.Conn.LocalAddr())

}

/*
You can run this with
./agentssh -bastion jump.example.com -host lanweb01
*/