Adds optional shared-secret authentication for /webhooks/nextcloud,
addressing the security follow-up flagged in #747.
Behavior:
- WEBHOOK_SECRET set: registrations pass authMethod="header" with
authData={"Authorization": "Bearer <secret>"} (encrypted at-rest in
Nextcloud's DB and forwarded on every delivery). The receiver
validates the same header with hmac.compare_digest before parsing
any payload; missing/invalid → 401.
- WEBHOOK_SECRET unset: registrations stay on authMethod="none" and
the receiver accepts unauthenticated POSTs (logging a one-time
startup warning). Backward compatible — operators can roll out at
their own pace.
Implementation notes:
- WebhooksClient.create_webhook gains an `auth_data` parameter mapped
to NC's `authData` body field; this is distinct from the existing
`headers` parameter (`headers` is plaintext static request headers,
`authData` is encrypted at-rest in NC and only emitted when
authMethod="header"). The previous `auth_method="bearer"` mention in
the docstring was incorrect — NC supports only "none" and "header".
- A small `webhook_auth_pair()` helper in auth/webhook_routes.py
centralises the secret→(auth_method, auth_data) resolution so the
preset flow and the Astrolabe-facing /api/v1/webhooks endpoint stay
in sync.
Also addresses the smaller review points from #747:
- f-string → lazy %s formatting in webhook_receiver.py and
webhook_routes.py.
- Move `int(time)` inside webhook_parser's try/except so a malformed
`time` field returns None instead of raising ValueError.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
