[OpenID] How to prove identity without leaving RP?

[SitG Admin]

>in this scenario, user first visits the OP; what I had in mind is 
>more: is it possible for a user to submit his credentials directly 
>on the RP page (even if the login form is an iframe to the OP or any 
>other 'clever' mechanism)

Maybe a pop-up window? But that doesn't neatly fit the "never leaving 
that page" idea. I'd consider it safe if you were using a password 
that only applied to THAT site (so a malicious site couldn't use the 
credentials even if it stole them), but that sort of destroys the 
whole single-sign-on idea :)

-Shade