Golang JWT Example. https://go.dev/play/p/RLiv9cD0f5-

jwt.go

package main

import (
	"errors"
	"fmt"
	"time"

	"github.com/golang-jwt/jwt/v5"
)

func Sign(key []byte, val string, ttl int64) (string, error) {
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.MapClaims{
		"val": val,
		"exp": time.Now().Unix() + ttl,
	})

	return token.SignedString(key)
}

func Parse(key []byte, token string) (string, error) {
	t, err := jwt.Parse(token, func(t *jwt.Token) (interface{}, error) {
		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("unexpected signing method: %v", t.Header["alg"])
		}
		return key, nil
	})

	if claims, ok := t.Claims.(jwt.MapClaims); ok && t.Valid {
		val, exists := claims["val"]

		if !exists {
			return "", errors.New("the field val does not exist")
		}

		return val.(string), nil
	}

	return "", errors.Join(err, errors.New("invalid token"))
}

func main() {
	secret := "the jwt secret"
	value := "The value to store in the token."

	token, err := Sign([]byte(secret), value, 1800)
	fmt.Println("Token:", token, err)

	result, err := Parse([]byte(secret), token)
	fmt.Println("Result:", result, err)
}