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Verify Webhook Signatures Correctly: HMAC-SHA256, Raw Body, Timestamps and Constant-Time Compare

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Self-Hosting & Infra intermediate 6 min read $0.01 Updated 2026-10-20

Tested in Python and Node: a verifier that returns ok, bad or stale; failures after re-serializing JSON, tampering, wrong secret and old timestamp; compare_digest and timingSafeEqual behaviors including the length-mismatch exception.

Accept webhooks only from the sender. Compute HMAC-SHA256 over the exact raw body plus timestamp, compare with a constant-time function, reject stale requests and avoid the reserialization bug.

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#webhooks#hmac#security#python#nodejs

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