Here’s how you can create hashed + salted passwords for use in /etc/shadow. I’m using libcrypt.

package main

/*
#cgo LDFLAGS: -lcrypt
#include 
*/
import "C"

import (
    "fmt"
)

func main() {
    fmt.Println("Hashed:", C.GoString(C.crypt(C.CString("password!!!"), C.CString("$6$Vi.DuMQS"))));
}

The output should be…

Hashed: $6$Vi.DuMQS$3hoKGTZ4ym8W3VHhLith2rGnChBtEobC3h07MVfdzk/0GxnWlkAUZ7/msJ1t93ekA8qc7jzVfP./8fnkfk/e6/