refactor: verify 응답에서 userId 제거

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/auth/handler.go

@@ -89,13 +89,12 @@ func (h *Handler) VerifyToken(c *fiber.Ctx) error {
 		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "token 필드가 필요합니다"})
 	}
 
-	userID, username, err := h.svc.VerifyToken(req.Token)
+	username, err := h.svc.VerifyToken(req.Token)
 	if err != nil {
 		return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": err.Error()})
 	}
 
 	return c.JSON(fiber.Map{
-		"userId":   userID,
 		"username": username,
 	})
 }

internal/auth/service.go

@@ -92,8 +92,8 @@ func (s *Service) Register(username, password string) error {
 	})
 }
 
-// VerifyToken validates a JWT and its Redis session, returning (userID, username, error).
-func (s *Service) VerifyToken(tokenStr string) (uint, string, error) {
+// VerifyToken validates a JWT and its Redis session, returning (username, error).
+func (s *Service) VerifyToken(tokenStr string) (string, error) {
 	token, err := jwt.ParseWithClaims(tokenStr, &Claims{}, func(t *jwt.Token) (any, error) {
 		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
 			return nil, fmt.Errorf("unexpected signing method")
@@ -101,21 +101,21 @@ func (s *Service) VerifyToken(tokenStr string) (uint, string, error) {
 		return []byte(config.C.JWTSecret), nil
 	})
 	if err != nil || !token.Valid {
-		return 0, "", fmt.Errorf("유효하지 않은 토큰입니다")
+		return "", fmt.Errorf("유효하지 않은 토큰입니다")
 	}
 
 	claims, ok := token.Claims.(*Claims)
 	if !ok {
-		return 0, "", fmt.Errorf("토큰 파싱 실패")
+		return "", fmt.Errorf("토큰 파싱 실패")
 	}
 
 	key := fmt.Sprintf("session:%d", claims.UserID)
 	stored, err := s.rdb.Get(context.Background(), key).Result()
 	if err != nil || stored != tokenStr {
-		return 0, "", fmt.Errorf("만료되었거나 로그아웃된 세션입니다")
+		return "", fmt.Errorf("만료되었거나 로그아웃된 세션입니다")
 	}
 
-	return claims.UserID, claims.Username, nil
+	return claims.Username, nil
 }
 
 func (s *Service) EnsureAdmin(username, password string) error {