Forward Deployed Engineer interview question · Most asked
How do you securely receive webhooks from a customer system?
Summary
Verify the HMAC signature over the raw body with a constant-time comparison, reject stale timestamps to prevent replay, acknowledge quickly and process asynchronously, deduplicate by event ID because senders retry, and don't rely on event order; fetch current state when it matters.
Longer Answer
Rotate signing secrets with an overlap period, restrict source IPs if the sender publishes them, and alert on signature failures.
Key Points
- Verify signature and timestamp.
- Fast ack, async processing.
- Idempotent by event ID.
- Don't trust ordering.
Explanation
What interviewers look for
Security and delivery semantics together.
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