As I stated in an earlier post, I taught an Android course this semester, and one team created an app called HU Pal that gives students access to their class schedule and chapel attendance information. This info is normally locked in an online system called Pipeline which requires users to login with a username and password. Once you have given HU Pal your username and password, it logs into Pipeline automatically and scrapes the information from a couple of web pages.
Brent Ward, one of the developers of the HU Pal app, wrote a document detailing how they created their app to login to Pipeline and screen-scrape personal information from web pages using jsoup. You can download the document here. Although the information in the document is specific to Pipeline, the techniques they describe can be generalized to any online system that requires user authentication.