Verify Webhook Signatures with HMAC
Recompute the HMAC over the raw body and constant-time compare so a forged webhook from a spoofed source is rejected.
Task
Implement const sig = crypto.createHmac('sha256', secret).update(rawBody).digest('hex'); so the service degrades gracefully under failure instead of cascading timeouts to callers.
When to use this
A downstream service slows down and without const sig = crypto.createHmac('sha256', secret).update(rawBody).digest('hex'); the upstream exhausts its thread pool in 12 seconds.
Prerequisites
- A service with inter-service calls or external dependencies
- A retry or circuit breaker library available
Steps
1. Configure const sig = crypto.createHmac('sha256', secret).update(rawBody).digest('hex'); in the project configuration file with the recommended defaults.
const sig = crypto.createHmac('sha256', secret).update(rawBody).digest('hex');
Expected output: The configuration is accepted and const sig = crypto.createHmac('sha256', secret).update(rawBody).digest('hex'); runs without errors on the first invocation.
2. Run the check locally to verify const sig = crypto.createHmac('sha256', secret).update(rawBody).digest('hex'); produces the expected result before pushing.
pnpm test
Expected output: Local run matches CI behavior; no surprises after push.
3. Add the gate to the CI pipeline so const sig = crypto.createHmac('sha256', secret).update(rawBody).digest('hex'); blocks merge on failure.
- name: Run add webhook signature verify
run: pnpm test
Expected output: Pull requests with failing const sig = crypto.createHmac('sha256', secret).update(rawBody).digest('hex'); are blocked from merging.
Troubleshooting
Problem
The check passes locally but fails in CI
Solution
Pin dependency versions and the runtime to match CI exactly; reproduce with the same Docker image or act.
Problem
Configuration is rejected with a schema error
Solution
Check the tool version matches the config schema; older versions may not support newer fields.
Limitations
- The gate only runs on events that trigger the workflow; locally pushed commits bypass it.
- Configuration drift is possible if someone edits settings outside version control.
Isolate failure
Start by measuring the problem. Recompute the HMAC over the raw body and constant-time compare so a forged webhook from a spoofed source is rejected. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run const sig = crypto.createHmac(‘sha256’, secret).update(rawBody).digest(‘hex’); against the current codebase and inspect the output before wiring it into CI.
const sig = crypto.createHmac('sha256', secret).update(rawBody).digest('hex');Verify graceful degradation
Once the gate is in place, make failures actionable. A failing const sig = crypto.createHmac(‘sha256’, secret).update(rawBody).digest(‘hex’); should point to the exact file and line, not a generic error. Pin the tool version in the lockfile so a upstream release does not silently change behavior. Review the gate output in every pull request just like a test result.