security: remediate vulnerabilities and issues from codebase audit

backend/middleware/auth.go

@@ -21,9 +21,10 @@ func AuthMiddleware(jwtSecret string) fiber.Handler {
 			}
 		}
 
-		// Fallback to query parameter for img/video tags
+		isQueryToken := false
 		if tokenString == "" {
 			tokenString = c.Query("token")
+			isQueryToken = true
 		}
 
 		if tokenString == "" {
@@ -52,6 +53,17 @@ func AuthMiddleware(jwtSecret string) fiber.Handler {
 			})
 		}
 
+		tokenType, _ := claims["type"].(string)
+		if isQueryToken {
+			if tokenType != "download" {
+				return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "invalid token type for query parameter"})
+			}
+		} else {
+			if tokenType != "access" {
+				return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "invalid token type for authorization header"})
+			}
+		}
+
 		c.Locals("userID", claims["sub"])
 		c.Locals("username", claims["username"])
 
@@ -86,3 +98,39 @@ func GenerateRefreshToken(userID int, username, secret string) (string, error) {
 	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
 	return token.SignedString([]byte(secret))
 }
+
+// GenerateDownloadToken creates a short-lived download token.
+func GenerateDownloadToken(userID int, username, secret string) (string, error) {
+	claims := jwt.MapClaims{
+		"sub":      userID,
+		"username": username,
+		"exp":      time.Now().Add(5 * time.Minute).Unix(),
+		"iat":      time.Now().Unix(),
+		"type":     "download",
+	}
+
+	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
+	return token.SignedString([]byte(secret))
+}
+
+// ValidateDownloadToken validates a download token
+func ValidateDownloadToken(tokenString, secret, expectedUsername string) error {
+	token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
+		return []byte(secret), nil
+	})
+
+	if err != nil || !token.Valid {
+		return fiber.NewError(fiber.StatusUnauthorized, "invalid token")
+	}
+
+	claims, ok := token.Claims.(jwt.MapClaims)
+	if !ok || claims["type"] != "download" {
+		return fiber.NewError(fiber.StatusUnauthorized, "invalid token claims")
+	}
+
+	if expectedUsername != "" && claims["username"] != expectedUsername {
+		return fiber.NewError(fiber.StatusUnauthorized, "token belongs to different context")
+	}
+
+	return nil
+}