jwt-dbg.go

package main

import (
	"bytes"
	"encoding/base64"
	"fmt"
	"io/ioutil"
	"os"
)

func die(v interface{}) {
	fmt.Fprintln(os.Stderr, v)
	os.Exit(1)
}

func main() {
	if len(os.Args) != 2 {
		die("usage: jwt-dbg -|file")
	}

	var (
		p   []byte
		err error
	)

	switch os.Args[1] {
	case "":
		die("no token file")
	case "-":
		p, err = ioutil.ReadAll(os.Stdin)
	default:
		p, err = ioutil.ReadFile(os.Args[1])
	}

	if err != nil {
		die(err)
	}

	pp := bytes.Split(p, []byte("."))

	if len(pp) != 3 {
		die("invalid token segments")
	}

	for _, p := range pp {
		for i := len(p) % 4; i > 0; i-- {
			p = append(p, '=')
		}

		p, err := base64.URLEncoding.DecodeString(string(p))
		if err != nil {
			die(err)
		}

		fmt.Println(string(p))
	}
}