package main

import (
	"encoding/base64"
	"fmt"
	"crypto/hmac"
    	"crypto/sha256"
)

// ValidMAC reports whether messageMAC is a valid HMAC tag for message.
func ValidMAC(message, messageMAC, key []byte) bool {
	mac := hmac.New(sha256.New, key)
	mac.Write(message)
	expectedMAC := mac.Sum(nil)
	return hmac.Equal(messageMAC, expectedMAC)
}

func main() {

	claimsEncode := "eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ"
	claims, _ := base64.RawURLEncoding.DecodeString(claimsEncode)
	fmt.Println(string(claims))
	
	headerEncode := "eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9"
	header, _ := base64.RawURLEncoding.DecodeString(headerEncode)
	fmt.Println(string(header))
	
	keyEncode := "AyM1SysPpbyDfgZld3umj1qzKObwVMkoqQ-EstJQLr_T-1qS0gZH75aKtMN3Yj0iPS4hcgUuTwjAzZr1Z9CAow"
	key, _ := base64.RawURLEncoding.DecodeString(keyEncode)
	
	sigEncode := "dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"
	sig, _ := base64.RawURLEncoding.DecodeString(sigEncode)
	msg := headerEncode + "." + claimsEncode
	fmt.Println(ValidMAC([]byte(msg), sig, key))
	
}