How to pull user private data from facebook given password?

I am trying to build a service that will centralize users' information. I know that Facebook, twitter, and LinkedIn would not give you chat histories and many other private information of a user. So I will be asking for users to prompt their password. The concept is that I will log in as users to pull the information. The question is how do I implement this feature to pull information from these sites. In our case, let's use Facebook as an example, how do I pull users' chats and send chats on behave of user with their password given?