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/lib/storage.ts

@@ -1,5 +1,5 @@
-import { S3Client, PutObjectCommand, DeleteObjectCommand } from "@aws-sdk/client-s3";
-import { getSignedUrl } from "@aws-sdk/s3-request-presigner";
+import { S3Client, DeleteObjectCommand } from "@aws-sdk/client-s3";
+import { createPresignedPost } from "@aws-sdk/s3-presigned-post";
 
 const bucket = process.env["STORAGE_BUCKET"] || "epicure-uploads";
 const endpoint = process.env["STORAGE_ENDPOINT"] || "http://localhost:9000";
@@ -32,9 +32,31 @@ const presignS3 = new S3Client({
   credentials,
 });
 
-export async function createPresignedUploadUrl(key: string, contentType: string): Promise<string> {
-  const command = new PutObjectCommand({ Bucket: bucket, Key: key, ContentType: contentType });
-  return getSignedUrl(presignS3, command, { expiresIn: 300 });
+/**
+ * A presigned PUT URL only signs Bucket/Key/ContentType — nothing binds the
+ * actual request body size to what the caller declared when it asked for the
+ * URL (and was charged storage-tier quota for), so a client could declare
+ * 1 byte and then PUT an arbitrarily large object. S3/MinIO's POST-policy
+ * upload flow is the fix: `content-length-range` is a *signed* condition,
+ * enforced by the storage server itself when it receives the upload — a
+ * mismatched Content-Length is rejected before the bytes are ever accepted,
+ * not just checked against something the client also controls.
+ */
+export async function createPresignedUploadPost(
+  key: string,
+  contentType: string,
+  maxBytes: number
+): Promise<{ url: string; fields: Record<string, string> }> {
+  return createPresignedPost(presignS3, {
+    Bucket: bucket,
+    Key: key,
+    Conditions: [
+      ["content-length-range", 0, maxBytes],
+      { "Content-Type": contentType },
+    ],
+    Fields: { "Content-Type": contentType },
+    Expires: 300,
+  });
 }
 
 export async function deleteObject(key: string): Promise<void> {
@@ -60,3 +82,8 @@ export function isOwnedRecipePhotoKey(key: string, recipeId: string, userId: str
 export function isOwnedReviewPhotoKey(key: string, recipeId: string, userId: string): boolean {
   return key.startsWith(`recipes/${recipeId}/reviews/${userId}-`);
 }
+
+/** Same rationale as isOwnedRecipePhotoKey, for the avatar-presign key prefix. */
+export function isOwnedAvatarKey(key: string, userId: string): boolean {
+  return key.startsWith(`user-avatars/${userId}/`);
+}