You want to ask the user for his password and check if it matches his current account's password before comitting an object?
You can take a look at the standard password validation logic in the default microflow ''ChangeMyPassword" and replicate/re-use this. Create your own screen (using an NP object like the AccountPasswordData object, or even the same object) and have the user enter a value, after which you could trigger similar functionality as in the mentioned microflow to check if it matches.. If they are the same, save the object.
From an UX standpoint why do you want to do this? The user has logged in so you already now it is him. But if you still want to make sure that it is him you might check out this module: https://appstore.home.mendix.com/link/app/105945/Finaps/2-Factor-Authentication-Module