golang connect sftp with ssh

sftp.go

package main

import (
	"fmt"
	"log"
	"os"

	"github.com/pkg/sftp"
	"golang.org/x/crypto/ssh"
	kh "golang.org/x/crypto/ssh/knownhosts"
)

func main() {
	user := "USER"
	address := "ADDRESS"
	port := "PORT"
	dirKey := "KEY.PEM" // directory file .pem or .cer

	privateKey, err := os.ReadFile(dirKey)
	if err != nil {
		log.Fatal("cannot get pem file")
	}

	signer, err := ssh.ParsePrivateKey(privateKey)
	if err != nil {
		log.Fatal(err)
	}

	homeDir := os.Getenv("HOME")
	hostKeyCallback, err := kh.New(homeDir+"/.ssh/known_hosts")
	if err != nil {
		log.Fatal("could not create hostkeycallback function :", err)
	}

	auths := []ssh.AuthMethod{ssh.PublicKeys(signer)}

	cfg := &ssh.ClientConfig{
		User:            user,
		Auth:            auths,
		HostKeyCallback: hostKeyCallback,
	}
	cfg.SetDefaults()

	// create session ssh
	client, err := ssh.Dial("tcp", address+":"+port, cfg)
	if err != nil {
		log.Fatal(err)
	}

	session, err := client.NewSession()
	if err != nil {
		log.Fatal(err)
	}

	defer session.Close()
	log.Println("we have a session")

	// create new sftp client
	sc, err := sftp.NewClient(client)
	if err != nil {
		fmt.Sprint(os.Stderr, "Unable to start SFTP subsystem : %v\n", err)
		os.Exit(1)
	}
	defer sc.Close()
	log.Println("connect to sftp")

}