In AngularFire you were able to access the providers (e.g Google) accessToken for the authenticated user.
There does not seem to be a way to access this with AngularFire
This works for me:
this.af.auth.getAuth().auth.getToken(false);//true if you want to force token refresh
You can put it into a Service and then you can get the token like this:
this.authService.getToken().then( (token) => console.debug(`******** Token: ${token}`));