fix: TRUST_PROXY-Kommentar aktualisieren und Modus beim Start loggen

Die Kommentare beschrieben noch einen einzelnen Reverse-Proxy-Hop. Sie
beschreiben jetzt die Cloudflare/Traefik-Liste. Beim Start wird einmal
auf info-Level geloggt, ob Hop-Zahl, Liste oder der Default aktiv ist
(nur Anzahl, keine Adressen), damit eine fehlende Produktionseinstellung
auffaellt. Das Standardverhalten bleibt unveraendert.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/src/app.config.ts

@@ -1,4 +1,9 @@
-import { RequestMethod, ValidationPipe, VersioningType } from '@nestjs/common';
+import {
+  Logger,
+  RequestMethod,
+  ValidationPipe,
+  VersioningType,
+} from '@nestjs/common';
 import { NestExpressApplication } from '@nestjs/platform-express';
 import helmet from 'helmet';
 import cookieParser from 'cookie-parser';
@@ -7,11 +12,15 @@ import { requestLoggerMiddleware } from './common/middleware/request-logger.midd
 import { noStoreMiddleware } from './common/middleware/no-store.middleware';
 
 /**
- * How many reverse-proxy hops to trust for X-Forwarded-For. It decides the
- * client IP behind every rate limit and API-key IP allowlist: too few and
- * all users share the proxy's IP, too many and a client can forge its own.
- * A hop count ("1", the single K8s ingress) or Express' list syntax
- * ("loopback, 10.0.0.0/8").
+ * Which proxies to trust for X-Forwarded-For. It decides the client IP behind
+ * every rate limit and API-key IP allowlist: trust too little and all users
+ * share the proxy's IP, trust too much and a client can forge its own.
+ *
+ * Production runs client -> Cloudflare -> Traefik -> backend, so the hop
+ * count is not stable; TRUST_PROXY is an Express list there ("loopback,
+ * 10.42.0.0/16, <Cloudflare IPv4+IPv6 ranges>", see
+ * deploy/k8s/backend/configmap.example.yaml). A plain number ("1") is a hop
+ * count and stays the default when the variable is unset.
  */
 export function trustProxySetting(): number | string {
   const raw = process.env.TRUST_PROXY?.trim();
@@ -21,11 +30,29 @@ export function trustProxySetting(): number | string {
   return /^\d+$/.test(raw) ? Number(raw) : raw;
 }
 
+/** Startup log line for the active mode; never includes the addresses. */
+export function describeTrustProxy(
+  setting: number | string,
+  isExplicit: boolean,
+): string {
+  if (typeof setting === 'number') {
+    return isExplicit
+      ? `TRUST_PROXY: ${setting} trusted hop(s)`
+      : `TRUST_PROXY not set, using default of ${setting} trusted hop`;
+  }
+  const entries = setting.split(',').filter((e) => e.trim()).length;
+  return `TRUST_PROXY: list of ${entries} trusted proxy range(s)`;
+}
+
 export function configureApp(app: NestExpressApplication): void {
-  // Trust the single reverse-proxy hop (K8s ingress) so req.ip reflects the
+  // Trust the configured proxies (Traefik, Cloudflare) so req.ip reflects the
   // real client IP from X-Forwarded-For — required for per-client throttling
   // to work correctly rather than rate-limiting all traffic together.
-  app.set('trust proxy', trustProxySetting());
+  const trustProxy = trustProxySetting();
+  app.set('trust proxy', trustProxy);
+  new Logger('Bootstrap').log(
+    describeTrustProxy(trustProxy, !!process.env.TRUST_PROXY?.trim()),
+  );
   // No ETags: they let caches and proxies revalidate (and keep) personal
   // responses that are meant to be no-store.
   app.set('etag', false);