Custom Events should be schema agnostic
When I first read about the idea of custom events, I would expect to ingest any kind of event, straight from the producer to event grid topic without any transformation required.
In example, if I want to receive a commit event from github via webhook to Event Grid, I have to receive it through a middleware(azure function) to parse it to EventGrid expected schema, otherwise it will fail, and this brings a lot extra work that should not be necessary, also makes my producer coupled with Event Grid.
If I have to build up all these things to make the event processing reliable, I would prefer to receive the event in a function, delivery it to a queue and then have a function to process it from the queue.
I would expect to register the event grid topic as a web-hook on github and have the exact event sent from GitHub received in the topic, and them delivered to the function\queue subscribed to that topic without any transformation.
Another point is that the authentication should be more flexible, that I raised in a separate feedback.