Request Body Validation

I am getting started with Istio. One of my use-cases is implementing an api gateway. Going through the Isito documentation I am a bit confused on which service or component is responsible for validating requests.

The type of request validation that I’m looking to implement is body validation (like validating a JSON POST request) at the api gateway level before sending traffic upstream to other services.

I took a look at the Traffic Management references but I’m not really sure where to start with this. Is there a combination of components that can achieve this? Is it even something I can do with Istio? Thank you.