Transloadit

What is Signature Authentication for Notification?

Signature Authentication for Notification lets a back end verify the authenticity and integrity of Notifications sent by Transloadit. Each notification is a form-encoded POST whose transloadit field carries the Assembly Status JSON as a string and whose signature field carries an HMAC of that string computed with the Workspace’s Auth Secret.

How Signature Authentication for Notification works

When a processing notification reaches a webhook endpoint, the receiver recomputes the authentication value from the verbatim transloadit form field and compares it with the signature field before trusting the parsed event. Signatures prefixed with an algorithm name in the form algo:signature identify the hash used, while unprefixed values are legacy SHA-1 signatures. Verification protects integrity and origin authentication but does not by itself guarantee that a valid delivery is new, so it is the first stage in a webhook pipeline, ahead of idempotency checks, job lookup, and side effects.

Key facts

  1. The signature covers only the JSON string delivered in the transloadit form field, not the raw HTTP request body, so verification works after ordinary form parsing as long as the field value is hashed verbatim.
  2. A constant-time comparison avoids leaking how much of a supplied signature matched, and malformed encodings should be rejected before any business action occurs.
  3. A valid notification can be delivered more than once during retries; verification must be paired with an idempotency key or recorded event identity to prevent duplicate effects.

When Signature Authentication for Notification matters

Verify every notification before updating records or triggering downstream work: parse the form, compute the HMAC over the exact transloadit field value, and compare it with the supplied signature. Never JSON-parse and re-serialize the payload before verifying, because a re-serialized string will not match the bytes that were signed.

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