Basically all the guides show you how to use the generator to create a basic authentication system. But in real life there may be a need to add other fields to the user such as first_name, last_name, phone, address, country_id (fk to a countries table...)
Is this even possible with this generator? Or should I look into writing my own system from scratch?
The generator gives you the very basic needed for Authentication. If you need to add more things to your user, you can always modify the class.