How to retrieve AD Informations from Custom Application Page (Using VB)

I've just created a new application page (aspx with VB). I can't find any solution to gather their AD informations (specific attributes) without asking them their password twice (first time when they login).

I'm not a dev, so I must miss something. When I create the context ('ctx') I must use their password as an argument. I would like to avoid asking them.