If you REALLY need some kind of popup for checking the logon details, then you just build it. It should not be that hard. Perhaps simple screen with two input fields (user ID and password) and then just confirm with function module SUSR_LOGIC_CHECK_RFC whether the entered values were correct. You could call/open this popup when the user clicks the work item (the popup logic needs to be in the method that gets called from the task.)
I am sure that there might be even easier solutions. But in any case I doubt that there are some kind of standard solution - you need to build it by yourself, which should not be that hard.
Kind regards,
Karri