Use subject claim for user id

internal/auth/manager.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"strconv"
 	"time"
 
 	"github.com/golang-jwt/jwt/v5"
@@ -18,7 +19,6 @@ var (
 
 // Claims represents the JWT claims structure
 type Claims struct {
-	UserID int64  `json:"user_id"`
 	Email string `json:"email"`
 	jwt.RegisteredClaims
 }
@@ -38,9 +38,9 @@ func NewJWTManager(secretKey string, tokenDuration time.Duration) *JWTManager {
 // GenerateToken creates a new JWT token for a user
 func (m *JWTManager) GenerateToken(userID int64, email string) (string, error) {
 	claims := Claims{
-		UserID: userID,
 		Email: email,
 		RegisteredClaims: jwt.RegisteredClaims{
+			Subject:   strconv.FormatInt(userID, 10),
 			ExpiresAt: jwt.NewNumericDate(time.Now().Add(m.tokenDuration)),
 			IssuedAt:  jwt.NewNumericDate(time.Now()),
 			NotBefore: jwt.NewNumericDate(time.Now()),
@@ -97,5 +97,9 @@ func (m *JWTManager) RefreshToken(tokenString string) (string, error) {
 		return "", err
 	}
 
-	return m.GenerateToken(claims.UserID, claims.Email)
+	userId, err := strconv.ParseInt(claims.Subject, 10, 64)
+	if err != nil {
+		return "", err
+	}
+	return m.GenerateToken(userId, claims.Email)
 }