Event dict in webhook mapping

I am trying to enable webhook notifications to telegram for when someone logs in successfully or fails login. I've set up the transport, the notification rules, it triggers the notification successfully on logins and fails.

What I am missing is how to add more info to the webhook payload? I want to add the client IP for failed logins, for example, among other things.
I tried making a custom webhook mapping, and extracting info from request.context.event, but event dict doesn't seem to be available in this scope.

In the documentation there is only a single example that uses request.context['notification']. That doesn't contain the info I need.
Is there a way to get the event here and access that info?