IDM-11: Use an XSEDE identity for InCommon authentication

Executive Summary: 
A researcher wants to authenticate to a national CI service that accepts InCommon identities.
User Importance Summary: 
This use case allows researchers who are NOT at InCommon-participating institutions to use their XSEDE identity to authenticate to national CI resources that accept or require InCommon identities.
Target Communities and Sizes: 
Researchers at non-R01 institutions who use XSEDE - 100 < N < 999