Storing user details from Google Sign-In to RTDB

Question

So I have a React application setup with firebase.

I have two auth methods (Email password & Google Auth).

We have some custom parameters that needs to be assigned to the user, so we are using rtdb for that. Hence when user signs in through email and password, we simply store that in the rtdb when auth is successful.

But how can I achieve the same with Google Auth in firebase? I just want to save the email and some additional parameters in rtdb once the user signs in for the first time through Google (it shouldn't be invoked from the second time user signs in).