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/app/api/v1/users/me/route.ts

@@ -5,6 +5,7 @@ import { db, users, eq } from "@epicure/db";
 import { z } from "zod";
 import { gravatarUrl } from "@/lib/gravatar";
 import { USERNAME_PATTERN, isUsernameTaken } from "@/lib/username";
+import { isOwnedAvatarKey, getPublicUrl } from "@/lib/storage";
 
 const PatchSchema = z.object({
   name: z.string().min(1).max(100).optional(),
@@ -13,9 +14,12 @@ const PatchSchema = z.object({
   privateBio: z.string().max(2000).optional().nullable(),
   isPrivate: z.boolean().optional(),
   username: z.string().trim().toLowerCase().regex(USERNAME_PATTERN, "3-20 characters, lowercase letters, numbers, and underscores only").optional(),
-  // A custom-uploaded avatar URL, or null to revert to the initials fallback
-  // (or Gravatar, if useGravatar is on — see below).
-  avatarUrl: z.string().url().max(2048).optional().nullable(),
+  // The storage key returned by /api/v1/upload/avatar-presign (not a URL) —
+  // the server validates it was actually issued to this user and builds the
+  // public URL itself, so a client can't point avatarUrl at an arbitrary or
+  // another user's object. `null` reverts to the initials fallback (or
+  // Gravatar, if useGravatar is on — see below).
+  avatarKey: z.string().max(500).optional().nullable(),
   // Off by default (Settings → Profile) — Gravatar is looked up by an MD5
   // hash of the user's email, sent to a third party.
   useGravatar: z.boolean().optional(),
@@ -32,7 +36,7 @@ export async function PATCH(req: Request) {
     return NextResponse.json({ error: "Username already taken" }, { status: 409 });
   }
 
-  const { avatarUrl, useGravatar, ...rest } = body.data;
+  const { avatarKey, useGravatar, ...rest } = body.data;
   const updates: Partial<typeof users.$inferInsert> = { ...rest };
 
   // useGravatar is only ever toggled from the settings form, never alongside
@@ -45,13 +49,16 @@ export async function PATCH(req: Request) {
     }
   }
 
-  if (avatarUrl !== undefined) {
-    if (avatarUrl === null) {
+  if (avatarKey !== undefined) {
+    if (avatarKey === null) {
       const gravatarOptedIn = useGravatar ?? (await getUseGravatar(session.user.id));
       updates.avatarUrl = gravatarOptedIn ? gravatarUrl(session.user.email) : null;
       updates.hasCustomAvatar = false;
     } else {
-      updates.avatarUrl = avatarUrl;
+      if (!isOwnedAvatarKey(avatarKey, session.user.id)) {
+        return NextResponse.json({ error: "Invalid avatar key" }, { status: 400 });
+      }
+      updates.avatarUrl = getPublicUrl(avatarKey);
       updates.hasCustomAvatar = true;
     }
   }