An OPTIONAL shared token so the app can be used off-LAN (via the relay/tunnel) more
safely than "anyone who reaches the port gets a shell". Sits IN FRONT OF the existing
Origin/CSRF model — never replacing it — and is fully inert when unset.
- src/http/auth.ts (new, pure): constantTimeEqual hashes both inputs to sha256 (32
bytes) then crypto.timingSafeEqual — no `===`, no length side-channel, never throws.
parseCookieHeader / cookieIsAuthed / buildSetCookie / isAuthEnabled.
- WEBTERM_TOKEN in config: 16–512 URL/cookie-safe chars or the server refuses to start.
- GET /?token=<t> or POST /auth (rate-limited 10/min) validates → sets
HttpOnly; SameSite=Strict; Secure-when-https cookie; public/login.html (no <script>).
- When enabled: the WS handshake (AFTER the Origin check, before handleUpgrade) + a
central authGate over all remote HTTP require the cookie. Open: /login, /auth.
Loopback bypass scoped to /hook* ONLY (tighter than the plan — gates the local
browser too).
- Unset ⇒ isAuthEnabled false ⇒ pure passthrough (LAN zero-config unchanged).
Honest tradeoff (in code + CLAUDE.md + login page): a bar-raiser, NOT a TLS/Tailscale
substitute — on bare ws:// the token is cleartext + replayable; only hardens the
TLS-terminated relay path. Verified: typecheck + build:web clean, 2118 pass at
--test-timeout=30000 (disabled-mode regression proven; only the known tmux flake red);
auth.ts 100% line coverage.
