security: fix full audit findings (v0.32.0)

Full list of the audit's confirmed findings and their fixes:

- Stored XSS via unescaped JSON-LD on the public recipe page
  (app/r/[id]/page.tsx) — escape < before injecting.
- CSP allowed unsafe-eval in production — now dev-only (Next prod
  never eval()s; only its HMR does).
- avatarUrl accepted any URL with no ownership check — now takes an
  avatarKey issued by avatar-presign, validated server-side, same
  pattern as recipe/review photos.
- No session revocation on password change/reset — both now revoke
  other sessions (revokeOtherSessions: true, revokeSessionsOnPasswordReset).
- Rate-limit bypass via spoofable X-Forwarded-For — take the last
  (proxy-appended) hop instead of the first (client-supplied) one,
  matching the single-Traefik-hop topology.
- Webhook signing secrets stored plaintext — now AES-256-GCM
  encrypted like every other secret in this app, with a legacy-
  plaintext fallback for pre-existing rows (bare hex has no ":", our
  ciphertext format always does).
- Better Auth's own rate limiter defaulted to in-memory storage,
  ineffective across replicas — now backed by the same Redis as
  lib/rate-limit.ts (secondaryStorage), with storeSessionInDatabase
  explicit so session storage itself doesn't move as a side effect.
- Presigned upload URLs didn't bind the declared file size to the
  actual upload, letting a client under-declare size (and quota
  charge) then PUT an arbitrarily large object — switched to S3
  presigned POST with a signed content-length-range condition,
  enforced by the storage server itself.
- generateMetadata() on the recipe page skipped the visibility
  filter the page body uses, leaking a private recipe's title via
  <title> to any signed-in user with the id.
- Block/unblock had no rate limit, unlike follow/unfollow.
- AI quota was charged even when a user's own BYOK key was used
  (their own credentials/billing) — added an isByok flag through
  the config-resolution chain and skip the charge when set. Also
  wired BYOK into generate/generate-from-idea/translate/import-url,
  which never looked it up at all before.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/proxy.ts

@@ -18,9 +18,21 @@ const IP_RATE_LIMITED_PATHS = ["/r/", "/s/"];
 const IP_RATE_LIMIT = 60;
 const IP_RATE_LIMIT_WINDOW_SECONDS = 60;
 
+// Epicure sits behind exactly one reverse proxy (Traefik — see traefik/epicure.yml).
+// Each hop *appends* the address it saw to X-Forwarded-For, so with a single
+// trusted hop in front of us, the rightmost entry is the address Traefik itself
+// observed — i.e. the real client — while anything to its left (including the
+// entire header, on a direct request with no proxy at all) is attacker-supplied
+// and must not be trusted. Taking the leftmost entry, as before, let a client
+// set an arbitrary X-Forwarded-For and get a fresh rate-limit bucket on every
+// request. If another reverse proxy is ever added in front of Traefik, this
+// needs to pop one more entry per added hop.
 function getClientIp(request: NextRequest): string {
   const forwardedFor = request.headers.get("x-forwarded-for");
-  if (forwardedFor) return forwardedFor.split(",")[0]!.trim();
+  if (forwardedFor) {
+    const parts = forwardedFor.split(",");
+    return parts[parts.length - 1]!.trim();
+  }
   return request.headers.get("x-real-ip") ?? "unknown";
 }