login method
logs the user in and updates the UI
Implementation
Future login(String? username, String? password) async {
// current kürzel and password for testing are HH testpass
if (username == null || password == null) {
throw Exception(S.current!.usernameOrPasswordWasNotGiven);
}
var res = await API().login(User(username, password));
debugPrint('logged in, ${res.toString()}');
notifyListeners();
}