Authentication

การทำ Authentication ใน Go ด้วย JWT, OAuth, และ session-based auth

JWT (JSON Web Tokens)

go get github.com/golang-jwt/jwt/v5

package main

import (
    "fmt"
    "time"

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

var secretKey = []byte("my-super-secret-key-change-in-production")

type Claims struct {
    UserID int    `json:"user_id"`
    Email  string `json:"email"`
    Role   string `json:"role"`
    jwt.RegisteredClaims
}

func GenerateToken(userID int, email, role string) (string, error) {
    claims := Claims{
        UserID: userID,
        Email:  email,
        Role:   role,
        RegisteredClaims: jwt.RegisteredClaims{
            ExpiresAt: jwt.NewNumericDate(time.Now().Add(24 * time.Hour)),
            IssuedAt:  jwt.NewNumericDate(time.Now()),
            NotBefore: jwt.NewNumericDate(time.Now()),
            Issuer:    "my-app",
            Subject:   fmt.Sprintf("%d", userID),
        },
    }

    token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
    return token.SignedString(secretKey)
}

func ValidateToken(tokenString string) (*Claims, error) {
    token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (interface{}, error) {
        // Verify signing method
        if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
            return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
        }
        return secretKey, nil
    })

    if err != nil {
        return nil, err
    }

    if claims, ok := token.Claims.(*Claims); ok && token.Valid {
        return claims, nil
    }

    return nil, fmt.Errorf("invalid token")
}

func main() {
    // Generate token
    token, err := GenerateToken(123, "user@example.com", "admin")
    if err != nil {
        panic(err)
    }
    fmt.Println("Token:", token[:50], "...")

    // Validate token
    claims, err := ValidateToken(token)
    if err != nil {
        panic(err)
    }
    fmt.Printf("Claims: UserID=%d, Email=%s, Role=%s\n",
        claims.UserID, claims.Email, claims.Role)
}