Sounds interesting, but I wouldn't put the code for dialogs and dialog boxes into the second module. Maybe create a third module with those additions or one additional module per input method. Or leave that to the application creator and only provide a function to deliver username/password into the module.
Comment on Re: Names and ideas for new CPAN modules
The module that I want to use AutoProxy in wants it to have a basic (Unix shell) dialog. That dialog will almost certainly be replaceable by a GUI dialog box by wrapping/subclassing LWP::UA::AutoProxy (or whatever it ends up being called).