If an anonymous user tries to acces a form or microflow of the application that requires logging in first, a pop-up will appear with the username + password fields, and a login + cancel button. This pop-up can be styled using CSS, which is nice, but I would actually like to be able to modify the contents of this pop-up, as well. The main reason is that one of our customers would like to add a 'Register' button to this pop-up, so users can create a new account from there. I guess this is not currently possible (or is it?) through the modeler. Is there a way to modify it otherwise? And will 'system' forms/pop-ups like these eventually be made editable?
Though there are plans to make the login popup editable in the Modeler, currently the LoginForm widget from the AppStore is the best way to go. This widget should be added to a form accessible for anonymous users. The styling of the widget can be done with css, and additional content like a register button can also be added to the form.
Querijn, don't think this is possible trough the "normal" ways. Maybe the only way is to hack your way into the core. If you can find this login pop-up somewhere in the mendix install folder, you could add some custom features.