security: internal audit — batch 1

Fixes the critical + high + medium findings from our internal security
review. Bundled into one PR because the changes overlap heavily (JWT
verification unifies across three call sites; backup-code hashing and
demo-email handling cross-cut several services); splitting them out
would mean redundant reviews of the same files.

Critical
- CI-C1 — .github/workflows/test.yml: restore actions/{checkout,setup-
  node,upload-artifact} to @v4. The @v6 refs don't exist, so the test
  workflow was errorring before a single test ran.
- SEC-C1 — mfaPolicy now extracts the token via extractToken() (cookie-
  first, Bearer fallback). Previously it only read Authorization, so
  every cookie-authenticated SPA session bypassed require_mfa entirely.
- SEC-C2/C4/C6 — all JWT verification paths (MCP bearer, file download,
  photo route) now go through the shared verifyJwtAndLoadUser that
  checks password_version. resetPassword additionally deletes every
  mcp_tokens row and marks outstanding oauth_tokens revoked, so a
  password reset invalidates ALL credential classes — not just the
  cookie JWT.

High
- SEC-H2 — reset email URL is built from server-side APP_URL /
  ALLOWED_ORIGINS (via existing getAppUrl()), not request headers.
  Closes the host-header-injection vector into reset links.
- SEC-H3 — OIDC findOrCreateUser wraps the invite-redemption UPDATE +
  user INSERT in a transaction. The UPDATE is the capacity check; if
  a concurrent callback takes the last slot, the whole transaction
  aborts with registration_disabled instead of double-creating users.
- SEC-H4 — new verifyIdToken() performs full JWT signature
  verification via the provider's JWKS (Node's crypto.createPublicKey
  accepts JWK directly — no extra dependency), plus iss/aud/exp
  checks. The callback also rejects the login when userinfo.sub does
  not match id_token.sub.
- SEC-H5 — OAuth DCR now validates redirect_uris against an allowlist
  of schemes: https, http-loopback, or a private custom scheme. Plain
  http://non-loopback is rejected.
- SEC-H6 — oauthService audience defaults to mcpResource when the
  `resource` parameter is missing, so tokens are always audience-bound
  to /mcp instead of being issued with audience=null.
- SEC-H7 — HSTS is enabled any time NODE_ENV=production (previously
  required FORCE_HTTPS=true), includeSubDomains defaults on and can
  be disabled with HSTS_INCLUDE_SUBDOMAINS=false.
- SEC-H8 — trek_session cookie Secure flag is also driven by
  req.secure (which Express resolves from X-Forwarded-Proto once
  trust proxy is set), so instances behind a TLS-terminating proxy
  get Secure cookies without needing FORCE_HTTPS.

Medium
- SEC-M1 — permanentDeleteFile / emptyTrash / avatar unlink now use
  fs.promises.rm with { force: true } (one async op vs the previous
  existsSync + unlinkSync pair per file).
- SEC-M2 — invalidatePermissionsCache() is called inside restoreFromZip
  so a restored DB with different permission rows is honoured
  immediately.
- SEC-M3 + C1 — idempotency store bounds the key at 128 chars, caches
  only responses ≤ 256 KiB, and scopes the lookup by (key, user_id,
  method, path) rather than (key, user_id). Same key replayed against
  a different endpoint no longer returns a stale unrelated body.
- SEC-M4 — share_tokens gets an expires_at column; new tokens default
  to 90-day TTL, expired tokens are denied at lookup. Existing tokens
  stay NULL = no expiry so already-published links don't break.
- SEC-M5 — /uploads/photos/:filename now resolves the photo to its
  trip_id and requires the share token to cover THAT trip. Previously
  any share token for any trip would unlock any photo filename.
- SEC-M6 — BLOCKED_EXTENSIONS is the single source of truth shared
  between fileService and collab uploads. The '*' allowed_file_types
  wildcard now still rejects executables/scripts.
- SEC-M7 — single DEMO_EMAILS constant (services/demo.ts) used by
  demoUploadBlock, mfaPolicy, and every demo-mode guard in
  authService. The old demoUploadBlock only matched 'demo@nomad.app'
  so the seed 'demo@trek.app' could in fact upload in demo mode.
- SEC-M8 — MFA backup codes are now bcrypt-hashed at rest
  (hashBackupCodeBcrypt). matchBackupCode accepts both bcrypt and
  legacy SHA-256 hex hashes, so existing installs keep working until
  the user regenerates codes via enableMfa.
- SEC-M9 — document the "security via UUID v4 filename" model for
  /uploads/avatars|covers|journey. Requires no code change but
  captures the decision so future reviewers don't re-flag it.
- SEC-M10 — already covered by the resetPassword revocation logic
  above: mcp_tokens DELETE + oauth_tokens UPDATE … SET revoked_at.

Performance
- PERF-H1 — new migration adds the indexes flagged in the audit:
  trips(user_id), trips(created_at DESC), photos(day_id),
  photos(place_id), reservations(day_id), share_tokens(token), plus
  conditional day_accommodations and notifications indexes depending
  on which columns are present.

Tests
- tests/integration/oidc.test.ts now mocks verifyIdToken and passes
  an id_token in the exchangeCodeForToken stub for the three flows
  that exercise a successful callback. The three remaining failures
  tests pointed out were all pre-existing (file-upload flakes +
  notificationPreferences event_types count drift), none introduced
  by this PR.

server/src/app.ts

@@ -5,11 +5,9 @@ import cookieParser from 'cookie-parser';
 import path from 'node:path';
 import fs from 'node:fs';
 
-import jwt from 'jsonwebtoken';
-import { JWT_SECRET } from './config';
 import { logDebug, logWarn, logError } from './services/auditLog';
 import { enforceGlobalMfaPolicy } from './middleware/mfaPolicy';
-import { authenticate } from './middleware/auth';
+import { authenticate, verifyJwtAndLoadUser } from './middleware/auth';
 import { db } from './db/database';
 
 import authRoutes from './routes/auth';
@@ -76,6 +74,15 @@ export function createApp(): express.Application {
   }
 
   const shouldForceHttps = process.env.FORCE_HTTPS === 'true';
+  // HSTS is worth enabling any time we're serving production traffic,
+  // not only when FORCE_HTTPS is set. Self-hosters behind Traefik /
+  // Caddy / Cloudflare Tunnel typically leave FORCE_HTTPS unset (the
+  // proxy handles the redirect for them), and the previous "HSTS off by
+  // default" meant those instances never advertised HSTS at all.
+  // `HSTS_INCLUDE_SUBDOMAINS=false` lets operators with sibling
+  // subdomains on the same apex opt back out.
+  const hstsActive = shouldForceHttps || process.env.NODE_ENV === 'production';
+  const hstsIncludeSubdomains = process.env.HSTS_INCLUDE_SUBDOMAINS !== 'false';
 
   // RFC 8414 / RFC 9728: discovery docs are world-readable — open CORS regardless of deployment config
   app.use(
@@ -112,7 +119,7 @@ export function createApp(): express.Application {
       }
     },
     crossOriginEmbedderPolicy: false,
-    hsts: shouldForceHttps ? { maxAge: 31536000, includeSubDomains: false } : false,
+    hsts: hstsActive ? { maxAge: 31536000, includeSubDomains: hstsIncludeSubdomains } : false,
   }));
 
   if (shouldForceHttps) {
@@ -161,12 +168,33 @@ export function createApp(): express.Application {
     });
   }
 
-  // Static: avatars, covers, and journey photos
+  // Static: avatars, covers, and journey photos.
+  //
+  // Security model (audit SEC-M9): these paths are unauthenticated by
+  // design. All filenames are server-chosen UUID v4 (see `uuid()` in
+  // the multer storage config for avatars / covers / journey uploads),
+  // which gives each asset >122 bits of namespace entropy — not
+  // guessable via enumeration. An attacker would need to have already
+  // seen the URL (email, shared journey, etc.) to request the file.
+  //
+  // Moving these behind auth would also break:
+  //   - Unauthenticated trip-card rendering on public share links
+  //   - Journey public-share pages (/public/journey/:token)
+  //   - Email-embedded avatars
+  //
+  // The `/uploads/photos/...` route below is DIFFERENT: photo URLs are
+  // not embedded in unauthenticated UI contexts, so that endpoint IS
+  // gated (session JWT with pv, or a share token scoped to the photo's
+  // trip).
   app.use('/uploads/avatars', express.static(path.join(__dirname, '../uploads/avatars')));
   app.use('/uploads/covers', express.static(path.join(__dirname, '../uploads/covers')));
   app.use('/uploads/journey', express.static(path.join(__dirname, '../uploads/journey')));
 
-  // Photos require auth or valid share token
+  // Photos require either a valid logged-in session (via JWT with the
+  // password_version gate) OR a share token that covers the SPECIFIC
+  // photo's trip. Previously any share token for any trip could request
+  // any photo filename by UUID — fine in practice because UUIDs are
+  // unguessable, but the auth model was wrong.
   app.get('/uploads/photos/:filename', (req: Request, res: Response) => {
     const safeName = path.basename(req.params.filename);
     const filePath = path.join(__dirname, '../uploads/photos', safeName);
@@ -174,17 +202,28 @@ export function createApp(): express.Application {
     if (!resolved.startsWith(path.resolve(__dirname, '../uploads/photos'))) {
       return res.status(403).send('Forbidden');
     }
+    // existsSync here is cheap and avoids a sendFile error frame; kept
+    // sync because the handler is already short-lived.
     if (!fs.existsSync(resolved)) return res.status(404).send('Not found');
 
     const authHeader = req.headers.authorization;
-    const token = (req.query.token as string) || (authHeader?.startsWith('Bearer ') ? authHeader.slice(7) : null);
-    if (!token) return res.status(401).send('Authentication required');
+    const rawToken = (req.query.token as string) || (authHeader?.startsWith('Bearer ') ? authHeader.slice(7) : null);
+    if (!rawToken) return res.status(401).send('Authentication required');
 
-    try {
-      jwt.verify(token, JWT_SECRET, { algorithms: ['HS256'] });
-    } catch {
-      const shareRow = db.prepare('SELECT id FROM share_tokens WHERE token = ?').get(token);
-      if (!shareRow) return res.status(401).send('Authentication required');
+    // JWT session path (with pv check).
+    const user = verifyJwtAndLoadUser(rawToken);
+    if (user) return res.sendFile(resolved);
+
+    // Share-token path: require the token to cover the exact trip the
+    // photo belongs to. Expired tokens fall through to 401.
+    const photo = db.prepare('SELECT trip_id FROM photos WHERE filename = ?').get(safeName) as { trip_id: number } | undefined;
+    if (!photo) return res.status(401).send('Authentication required');
+
+    const share = db.prepare(
+      "SELECT trip_id FROM share_tokens WHERE token = ? AND (expires_at IS NULL OR expires_at > datetime('now'))"
+    ).get(rawToken) as { trip_id: number } | undefined;
+    if (!share || share.trip_id !== photo.trip_id) {
+      return res.status(401).send('Authentication required');
     }
     res.sendFile(resolved);
   });