Closes FUNCTIONAL_AUDIT.md §4 #1: WebRTC 1:1 calls had working
signaling but no NAT traversal, so calls between two peers behind
symmetric NAT (corporate firewalls, mobile carrier CGNAT, Incus
container default networking) failed silently after the SDP exchange.
Backend:
- GET /api/v1/config/webrtc (public) returns {iceServers: [...]}
built from WEBRTC_STUN_URLS / WEBRTC_TURN_URLS / *_USERNAME /
*_CREDENTIAL env vars. Half-config (URLs without creds, or vice
versa) deliberately omits the TURN block — a half-configured TURN
surfaces auth errors at call time instead of falling back cleanly
to STUN-only.
- 4 handler tests cover the matrix.
Frontend:
- services/api/webrtcConfig.ts caches the config for the page
lifetime and falls back to the historical hardcoded Google STUN
if the fetch fails.
- useWebRTC fetches at mount, hands iceServers synchronously to
every RTCPeerConnection, exposes a {hasTurn, loaded} hint.
- CallButton tooltip warns up-front when TURN isn't configured
instead of letting calls time out silently.
Ops:
- infra/coturn/turnserver.conf — annotated template with the SSRF-
safe denied-peer-ip ranges, prometheus exporter, TLS for TURNS,
static lt-cred-mech (REST-secret rotation deferred to v1.1).
- infra/coturn/README.md — Incus deploy walkthrough, smoke test
via turnutils_uclient, capacity rules of thumb.
- docs/ENV_VARIABLES.md gains a 13bis. WebRTC ICE servers section.
Coturn deployment itself is a separate ops action — this commit lands
the plumbing so the deploy can light up the path with zero code
changes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
b8eed72f96