Forbid the site's browsing to anyone but not to me

[eluser]Alhazred[/eluser]
I have to put online a website, but before to allow to anyone to use it, I need to test it online.

During the test I want that anyone will see a "work in progress" page, but I want to be able to use it normally.

I know that I could put a redirect to any view file or controller, but there are a lot, so I was thinking something different, something easier to set and unset.

I can't put a redirect only to the main controller because if in example some one writes
www.website.com/aboutus
he opens the "About us" page and from there he could use the menu to navigate.

I was thinking to put something into the index.php, where any request has to pass, but I don't know if it is possible to modify it to have what I need.

Do you have any suggestion?