How can I implement custom user authentication provider/service and froward response to backend?

[raphaelchaula]

Hi, I was reading the docs on API GATEWAY, but I couldn't find the solution for the problem:

What I am struggling to achieve is, I have multiple services on cloud run, and one service is the authentication, I want all the requests from clients that hit API GATEWAY to be redirected to this custom authentication service where I will access a token and session Id and use them accordingly to validate get user data from session data and froward these data to appropriate service it was calling.

I use gRPC in my API calls, so I would like to know how I can achieve this using GCP API Gateway.

Thanks!