Opaque login with oauth provider

We are making an integration of RocketChat to our React Native mobile application, so we need to find a way how we can login user to rocketchat automatically. We are using Keycloak and we managed to make it work as oauth provider, when user has to click on button, which redirects him to the KeyCloak login screen.

This is a good start, but we need to proceed the login automatically, because we are already logged in and have a Keycloak token, so we need some way to exchange the Keycloak token for rocketchat token.

Any advice on this?

The issue names no repository files or tests. Start by tracing the existing OAuth-provider button flow used by the React Native application and the Keycloak token handoff; done means supporting login with an existing Keycloak token without another redirect.