internal/authentication/authentication.go

// Package authentication provides JWT token generation functionality.
// It implements a simple authentication mechanism using HS256-signed JWTs
// with configurable issuer, expiration time, and signing secret.
// The package uses github.com/golang-jwt/jwt/v5 for token creation and signing.
package authentication

import (
	"time"

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

type Auth struct {
	jwtIssuer   string
	jwtTTL      time.Duration
	secretBytes []byte
	timeNowFunc func() time.Time
}

func NewAuth(jwtIssuer string, jwtTTL time.Duration, secret []byte) Auth {
	return Auth{
		jwtIssuer:   jwtIssuer,
		jwtTTL:      jwtTTL,
		secretBytes: secret,
		timeNowFunc: time.Now,
	}
}

func (a Auth) GenerateJWT() (string, error) {
	claims := jwt.RegisteredClaims{
		Issuer:    a.jwtIssuer,
		IssuedAt:  jwt.NewNumericDate(a.timeNowFunc()),
		ExpiresAt: jwt.NewNumericDate(a.timeNowFunc().Add(a.jwtTTL)),
	}
	return jwt.NewWithClaims(jwt.SigningMethodHS256, claims).SignedString(a.secretBytes)
}