Belegübersicht: fail-closed Portal-Scoping (R144)

Pentester R144 (fail-closed, kein Finding): listAll scopte ueber
'if (isCustomerPortal && customerId)'. Fiele customerId bei einem
Portal-Token mal falsy aus, rutschte er in den Staff-Zweig (alle
Belege).

Jetzt: Portal-Token wird IMMER gescoped; ohne customerId -> leere
Menge (customerIds=[]) statt undefined/Staff. In:[] kann nie matchen.
Aktuell nicht erreichbar (Portal-Token traegt immer customerId), aber
robuster.

Verifiziert: customerIds=[] -> 0 Belege.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/controllers/creditNote.controller.ts

@@ -50,13 +50,18 @@ function handleError(res: Response, error: unknown, fallback: string) {
 export async function listAll(req: AuthRequest, res: Response): Promise<void> {
   try {
     // Portal-User: nur eigene + vertretene Kunden MIT Vollmacht.
+    // Fail-closed (Pentest R144): Ein Portal-Token wird IMMER gescoped. Fehlt
+    // wider Erwarten die customerId (null/0), ergibt das eine LEERE Menge –
+    // nicht den Staff-Zweig (der alle Belege zeigen würde).
     let customerIds: number[] | undefined;
-    if (req.user?.isCustomerPortal && req.user.customerId) {
-      customerIds = [req.user.customerId];
-      const representedIds: number[] = (req.user as any).representedCustomerIds || [];
-      for (const repCustId of representedIds) {
-        if (await authorizationService.hasAuthorization(repCustId, req.user.customerId)) {
-          customerIds.push(repCustId);
+    if (req.user?.isCustomerPortal) {
+      customerIds = req.user.customerId ? [req.user.customerId] : [];
+      if (req.user.customerId) {
+        const representedIds: number[] = (req.user as any).representedCustomerIds || [];
+        for (const repCustId of representedIds) {
+          if (await authorizationService.hasAuthorization(repCustId, req.user.customerId)) {
+            customerIds.push(repCustId);
+          }
         }
       }
     }