Verifying a webhook signature

This guide walks you through how to verify request signatures on your server to prevent attackers from imitating valid webhook events.

Extracting the signature and event body

Each webhook event has an x-sha2-signature header. This header contains the webhook event’s signature in hexadecimal format.

Remember to use the raw event request body because the fields may be reordered if you first parse it from JSON.

📘

Use the raw event body and don't convert to an object first.

Compute the expected signature

A webhook event is valid if the signature from the header is equal to the expected signature you compute for it. Make sure signatures are both in binary or hexadecimal before comparing.

Example pseudocode

The following pseudocode might be useful for you:

fun verify_webhook_event_signature(webhook_event_request)
  signature_header_hexadecimal = webhook_event_request.get_header("x-sha2-signature")

  # Make sure to use the raw event body and not to convert it to an object first.
  raw_event_body = webhook_event_request.body_as_string

  # Compute the HMAC using the SHA256 algorithm and using your webhook's token as the key.
  expected_signature = hmac(algorithm="SHA256", key=webhook_token, data=raw_event_body)

  # Make sure signatures are both in binary, or both in hexadecimal, before comparing.
  signature_header = decode_hexadecimal(signature_header_hexadecimal)

  # compare computed signature to received signature.
  if compare(signature_header, expected_signature)
    # It is now safe to parse the event body.
    return parse_json(raw_event_body)
  else
    # Handle an invalid webhook event.
    error("Invalid webhook event")

Did this page help you?