One way of doing it.
Whenever the user makes the 1st request, check if he is logged in.
If not direct to the login page. After successfully logging in, redirect to the "home" page.
If logged in, redirect to the "home" page.
So you need to have, at a minimum, one login page and one home page (which has the actual GWT generated JS in it)
After logging in, you can use something like
GWT History Mechanism to let the user navigate between views.
