add auth module

backend/internal/auth/jwt.go

@@ -0,0 +1,50 @@
+package auth
+
+import (
+	"errors"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+	"github.com/google/uuid"
+)
+
+type Claims struct {
+	UserID uuid.UUID `json:"user_id"`
+	jwt.RegisteredClaims
+}
+
+func GenerateToken(userID uuid.UUID, secret []byte, expiry time.Duration) (string, error) {
+	if userID == uuid.Nil {
+		return "", errors.New("user ID cannot be nil")
+	}
+	if secret == nil {
+		return "", errors.New("JWT secret not set")
+	}
+
+	claims := Claims{
+		UserID: userID,
+		RegisteredClaims: jwt.RegisteredClaims{
+			ExpiresAt: jwt.NewNumericDate(time.Now().Add(expiry)),
+			IssuedAt:  jwt.NewNumericDate(time.Now()),
+		},
+	}
+
+	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
+	return token.SignedString(secret)
+}
+
+func ParseToken(tokenString string, secret []byte) (*Claims, error) {
+	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (interface{}, error) {
+		return secret, nil
+	}, jwt.WithValidMethods([]string{jwt.SigningMethodHS256.Alg()}))
+
+	if err != nil {
+		return nil, err
+	}
+
+	if claims, ok := token.Claims.(*Claims); ok && token.Valid {
+		return claims, nil
+	}
+
+	return nil, errors.New("invalid token claims")
+}