Ok, first, thanks for this clear programme. i've test some more complex ones, and this one is the most intuitive.
But i saw in those others php shells the following feature and i think it won't hurt to add it to your work.
In addition to the basic authentification, the page could filter the ip, forbiding acces from unknown places.
Excuse my poor english, and keep up your work !
I have a patch to add this feature and will be submitting it in the next few days.