the loginuser class uses a trait called AuthenticatesUsers
if you open that trait you will see the functions (this applies for other controllers)
Illuminate\Foundation\Auth\AuthenticatesUsers;
here is the trait code https://github.com/laravel/framework/blob/5.1/src/Illuminate/Foundation/Auth/AuthenticatesUsers.php
sorry for the bad format, im using my phone
also Auth::routes()
it just calls a function that returns the auth routes thats it (i think)