IDM-02: Login to XSEDE user portal with username/password

Executive Summary: 
An XSEDE user needs to login to the XSEDE User Portal (XUP) using his or her XSEDE username and password. We assume the user has already registered with XSEDE.
User Importance Summary: 
We need a way for the XSEDE system to identify individual human beings. Individual users need to be able to authenticate (prove their identity) to the system.
Target Communities and Sizes: 
Everyone who uses the XSEDE user portal - 1,000 < N < 9,999