Command (message/data) enrichment from UI to Event Bridge after cognito authorization

We are designing a asynchronous process. The flow of steps are,

1. user login in using hosted cognito login form, ui receives the idToken
2. user interacting with the form in UI - for ex: createUser
3. ui invokes REST api gateway endpoint, and sends the idToken from cognito
4. api gw validates the request with cognito using the idToken
5. after this step, we want to enrich the data and add userId and role from idToken to data. (We want to do this after the authorization step, not from ui)
6. api gw integrates with event bridge and send the command data to event bridge.

Need some suggestion on the step #4. How do we able to achieve this ?