Is there a way to get the response body of the REST service call in the app

Currently implementing an automation using java + appium for an app that has both Facebook/Google Login.

The login will call our own API service with Facebook/Google access token in the request body.
The response body will then print out the user id, access token, refresh token… etc.

The access token is useful when validating user data within the app, but I have problem getting the access token.

If I call the API using rest assured from back end, that basically means I login with the exact same user twice to get the 2nd access token instead of retrieving the access token in the app.

I wonder if there a good way to get the response body string of the REST service call I made when automate the login action in the app.