What causes a store webhook that trusts unverified callbacks?

The webhook endpoint grants entitlements from any POST it receives, without verifying the request actually came from the store or that it has not been replayed.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix a Store Webhook That Trusts Unverified Callbacks

Quick answer: Verify the webhook signature against the provider's secret, reject unsigned or stale events, and process each event idempotently by its event ID.

Your backend grants items or subscription status when it receives a store webhook, but anyone who learns the URL can POST a fake event and grant themselves anything. Verify the cryptographic signature the provider sends, and dedupe by event ID so replays do nothing.

How to fix it

1. Verify the signature

Validate the provider's signature header against your endpoint secret on every request and reject anything that fails. An unsigned or mismatched event is dropped before any grant.

2. Reject stale and duplicate events

Check the event timestamp against a small tolerance to block replays, and record processed event IDs so the same event is never applied twice.

3. Fail closed and log

If verification cannot complete, return an error and grant nothing, and log rejected attempts so you can spot forgery attempts against the endpoint.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every HTML5 error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

Reproduce it once with full context and the fix writes itself. The hunt is the expensive part.