Webhooks

In short: A webhook is a notification in which a service calls an address of your application as soon as something happens, for example a payment is completed.

In more detail: Instead of your application constantly asking (“polling”), the other service reports by itself. It sends an HTTP POST request with the event data to a URL you provided.

In Depth

• Check the signature: Anyone can call the URL. The sender signs the message (HMAC) and you verify the signature with a secret key.
• Answer quickly: Confirm with 2xx, do the work afterwards in the background.
• Retries: If the confirmation is missing, the sender sends again. Hence idempotence.
• Order: Events can arrive swapped.
• Local tests: Tunnel services forward webhooks to the development machine.

See also: Idempotence, Message queue