How would you verify a webhook signature and prevent replay in a Python API?

Verifies provider signatures over raw bytes, enforces freshness, and makes repeated delivery idempotent.

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I read the raw request bytes and verify the provider's signature with the configured endpoint secret before parsing or acting on the payload. For HMAC signatures I compute the expected digest with the documented algorithm and compare it with hmac.compare_digest. I reject missing, malformed, or invalid signatures with a generic response. Re-serializing parsed JSON is wrong because whitespace and field order can change the signed bytes.

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Verifies provider signatures over raw bytes, enforces freshness, and makes repeated delivery idempotent.

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Verifies provider signatures over raw bytes, enforces freshness, and makes repeated delivery idempotent.
I read the raw request bytes and verify the provider's signature with the configured endpoint secret before parsing or acting on the payload. For HMAC signatures I compute the expected digest with the documented algorithm and compare it with hmac.compare_digest. I reject missing, malformed, or invalid signatures with a generic response. Re-serializing parsed JSON is wrong because whitespace and field order can change the signed bytes.
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A valid signature proves authenticity and integrity, but a captured valid request may still be replayed. When the provider signs a timestamp, I enforce a bounded tolerance with a synchronized clock. I also store the provider's delivery or event id under a unique constraint so retries produce the same result rather than duplicate side effects. Signature validation happens before expensive parsing or queueing.

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Parsing and re-encoding JSON before verification
Treating a valid signature as replay protection
Doing irreversible work before deduplication

How would you verify a webhook signature and prevent replay in a Python API?

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