GRP-14: Use a group to control access within an external resource

Executive Summary: 
A community member needs to use an XSEDE group to control access within a non-XSEDE service. Notable reasons include: a campus or L3 service offers services to specific XSEDE users, a science gateway offers group-based access control to gateway functions or resources. The service must either have a “plugin” feature that allows it to use an external group service, or a “local file” feature that allows it to use local files containing user IDs as the basis for access control.
User Importance Summary: 
XSEDE community members need to be able to define arbitrary groups of people to which they can refer throughout the XSEDE system for authorization and communication purposes. Researchers need these groups to be visible/usable within science gateways and campus IT systems (in a campus bridging scenario) as well as within XSEDE services.
Target Communities and Sizes: 
Science gateway and application developers - 100 < N < 1000 Campus IT administrators involved in campus bridging - 100 < N < 1000 Independent resource providers - 10 < N < 100