Calculate HS256 with secret keys read from a file

HS256-public-pem.go

// https://auth0.com/blog/critical-vulnerabilities-in-json-web-token-libraries/.

package main

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"io/ioutil"
	"log"
)

func main() {
	src := []byte("YOUR-MESSAGE")

	key, err := ioutil.ReadFile("path-to-secret-key")
	if err != nil {
		log.Fatal(err)
	}
	mac := hmac.New(sha256.New, key)
	mac.Write(src)

	encoded := base64.StdEncoding.EncodeToString(mac.Sum(nil))
	fmt.Print(encoded)

}