This was recently answered by Jeffrey Walter on the Launch Developers slack channel (launch-developers.slack.com)
I'll summarize here:
Launch provides the ability to establish callbacks (Webhooks) that will be POSTED to when a subscribed audit event happens.
An Audit event is described as [resource]:[action] using the resources and actions shown below.
Subscriptions for callbacks are set up using the Launch API as shown here: Launch Callbacks via API