fix: use rightmost X-Forwarded-For entry and add per-email rate-limit dimension

Fixes an XFF-spoofing bypass of the flyer rate limiter (leftmost entry is
attacker-controlled, not proxy-verified) and adds a second rate-limit
dimension keyed on the submitted email so spamming one address still gets
blocked even if IP-based limiting is ever defeated. Also bounds the
in-memory rate-limit Map via a call-count-triggered sweep.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LhY1QhDXGWfyhrxaJvfpNt

app/api/familyguard-flyer/route.ts

@@ -8,23 +8,44 @@ const RATE_LIMIT_WINDOW_MS = 60 * 60 * 1000;
 const RATE_LIMIT_MAX = 3;
 const requestLog = new Map<string, number[]>();
 
-function isRateLimited(ip: string): boolean {
+let cleanupCounter = 0;
+const CLEANUP_INTERVAL = 500;
+
+function isRateLimited(key: string): boolean {
   const now = Date.now();
-  const timestamps = (requestLog.get(ip) ?? []).filter(
+
+  cleanupCounter++;
+  if (cleanupCounter >= CLEANUP_INTERVAL) {
+    cleanupCounter = 0;
+    for (const [k, timestamps] of requestLog) {
+      const fresh = timestamps.filter((t) => now - t < RATE_LIMIT_WINDOW_MS);
+      if (fresh.length === 0) requestLog.delete(k);
+      else requestLog.set(k, fresh);
+    }
+  }
+
+  const timestamps = (requestLog.get(key) ?? []).filter(
     (t) => now - t < RATE_LIMIT_WINDOW_MS
   );
   if (timestamps.length >= RATE_LIMIT_MAX) {
-    requestLog.set(ip, timestamps);
+    requestLog.set(key, timestamps);
     return true;
   }
   timestamps.push(now);
-  requestLog.set(ip, timestamps);
+  requestLog.set(key, timestamps);
   return false;
 }
 
+// Nimmt an, dass genau ein Reverse-Proxy vorgeschaltet ist, der die beobachtete
+// Peer-IP anhängt (nicht ersetzt), und dass die App nie unter Umgehung dieses
+// Proxys direkt erreichbar ist — falls das nicht zutrifft, fällt der Limiter auf
+// den gemeinsamen "unknown"-Bucket zurück, wird aber nicht umgehbar.
 function getClientIp(request: Request): string {
   const forwarded = request.headers.get("x-forwarded-for");
-  if (forwarded) return forwarded.split(",")[0].trim();
+  if (forwarded) {
+    const parts = forwarded.split(",").map((p) => p.trim()).filter(Boolean);
+    if (parts.length > 0) return parts[parts.length - 1];
+  }
   return "unknown";
 }
 
@@ -33,7 +54,7 @@ function isValidEmail(email: string): boolean {
 }
 
 export async function POST(request: Request) {
-  if (isRateLimited(getClientIp(request))) {
+  if (isRateLimited(`ip:${getClientIp(request)}`)) {
     return NextResponse.json(
       { ok: false, error: "Zu viele Anfragen. Bitte versuchen Sie es später erneut." },
       { status: 429 }
@@ -54,6 +75,12 @@ export async function POST(request: Request) {
       { status: 400 }
     );
   }
+  if (isRateLimited(`email:${email}`)) {
+    return NextResponse.json(
+      { ok: false, error: "Zu viele Anfragen. Bitte versuchen Sie es später erneut." },
+      { status: 429 }
+    );
+  }
   if (body.dsgvoEinwilligung !== true) {
     return NextResponse.json(
       { ok: false, error: "Bitte stimmen Sie der Datenverarbeitung zu" },