Standalone router for inbound Polar (merchant-of-record) deliveries.
No bearer-token dep — authenticity comes from the Standard Webhooks
HMAC instead. Wired up so it's safe to deploy dark: empty
POLAR_WEBHOOK_SECRET makes the endpoint return 503 (loud) rather than
accept unsigned events.
Behaviour
- Standard Webhooks signature verification: HMAC-SHA256 over
`{webhook-id}.{webhook-timestamp}.{body}`, base64 secret prefixed
whsec_, ±5min replay window, constant-time compare against any of
the space-separated v1 tokens.
- Idempotency via UNIQUE on polar_events.event_id — a replayed
webhook-id short-circuits to 200 "duplicate" without re-running.
- Event dispatch table covers the 10 events we subscribed to:
subscription.{created,active,updated,uncanceled} -> tier=paid +
persist polar_customer_id / polar_subscription_id.
subscription.revoked -> tier=free (customer id kept so a resub
matches the same User row).
canceled / past_due / order.* / refund.created -> audit only.
- Unknown event types are acked 200 + recorded; we don't want to 4xx
on something Polar adds in the future and trigger their retry loop.
Schema (migration 0018)
- users.polar_customer_id, users.polar_subscription_id (both nullable
String(64)); UNIQUE on polar_customer_id so two users can't claim
the same Polar identity.
- polar_events table: event_id (unique), event_type, received_at,
processed_at, error, raw payload (truncated to 16 KiB).
Tests
- 7 in tests/test_polar_webhook.py: bad signature -> 401, stale
timestamp -> 401, missing headers -> 400, subscription.active flips
tier to paid + stores IDs, subscription.revoked drops to free while
keeping customer link, replayed webhook-id is no-op, unknown event
is acked.
- Full suite: 212 passed, 5 skipped.
Operator next steps before saving the webhook in Polar
1. Pull this branch to prod and apply migration 0018.
2. Save the webhook in Polar pointing at
https://read.markets/api/polar/webhook — Polar will accept the
save even though our endpoint still 503s (no secret yet).
3. Copy the secret Polar reveals into the prod .env as
POLAR_WEBHOOK_SECRET=whsec_... and restart the app.
4. Trigger a test event from Polar's dashboard to confirm 200 OK.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Giorgio Gilestro
6c13f855e9