LoginController uses AuthenticatesUsers trait and the login() is there, so the first thing I did was to add my own login() in the LoginController, something like:

public function login(Request $request) {
    $ret = parent::login($request);

    // Do the writting to the log

    return $ret;

This didn't work... so then I turned to try a postLogin() function, but didn't work either, it simply didn't execute. This function is on the LoginController

public function postLogin() {
    // Do writting to the log