こちらのプログラムを Go で書き換えました。
Node.js: JWT のペイロード部をデコード
 Python3: JWT のペイロード部をデコード

decode_jwt.go

// ---------------------------------------------------------------
//
//	decode_jwt.go
//
//				  Feb/07/2021
// ---------------------------------------------------------------
package main

import (
	"fmt"
	"os"
	"strings"
	"io/ioutil"
	b64 "encoding/base64"
)

// ---------------------------------------------------------------
func decode_jwt_proc(str_token string) string {
	aaa := strings.Split (str_token,".")
	str_bbb := strings.Replace(aaa[1],"-","+",-1)
	str_ccc := strings.Replace(str_bbb,"_","/",-1)

	llx := len(str_ccc)
	nnx := ((4 - llx % 4) % 4)
	ssx := strings.Repeat("=" , nnx)
	str_ddd := strings.Join([]string{str_ccc,ssx},"")
	ppp, err :=  b64.StdEncoding.DecodeString(str_ddd)
	if err != nil {
		fmt.Fprintf (os.Stderr,"*** error *** StdEncoding.DecodeString ***\n")
		fmt.Println("error:", err)
		return "error"
	}

	uEnc := b64.URLEncoding.EncodeToString([]byte(ppp))
	decode, _ := b64.URLEncoding.DecodeString(uEnc)

	return string(decode)
}

// ---------------------------------------------------------------
func main() {

	fmt.Fprintf (os.Stderr,"*** 開始 ***\n")
	file_token := os.Args[1]
	fmt.Fprintf (os.Stderr,"file_token = " + file_token + "\n")

	buff,_ := ioutil.ReadFile(file_token)
	fmt.Fprintf (os.Stderr,"len(buff) = %d\n" , len(buff))

	json_str := decode_jwt_proc(string(buff))
	fmt.Println (json_str)

	fmt.Fprintf (os.Stderr,"*** 終了 ***\n")
}

// ---------------------------------------------------------------

実行方法

go run decode_jwt.go token01.txt | jq .