How to get username and password after log in when using cla

I have a scenario in which I need to get the user's username and password after they have been authenticated.   I am using claims based auth using the default Sitefinity auth service.

I thought I would inherit from the built in login control and hook into the LoggedIn event,  but when I inherit from LoginControl when I add the control to the designer in the admin site I get this message:

Login (backward compatibility) widget is not compatible with Claims Authentication mode, use Login instead. Learn more in our documentation

What control should I inherit from if I am using Claims based auth?   Or, is there an easier way to access the user's username and password?