GRP-09: Synchronize an external group

Executive Summary: 
A community member needs to synchronize a group in the XSEDE system with a group defined in a non-XSEDE system. One notable reason is so that XSEDE’s group-based access control mechanisms (use cases GRP-12, -13, -14) can reference a group that is primarily managed in another system. For example: A multi-institution research team uses the Open Science Grid’s VOMS service to define its membership, and an XSEDE L3 service provider at Indiana University wants to authorize jobs submitted by the team. The IU service provider has determined that it would be much less expensive to use an XSEDE group than to install a local VOMS instance and use it 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. In many cases, the groups of people are already defined and managed in another system and our community members need to be able to reference those definitions.
Target Communities and Sizes: 
XSEDE users who actively participate in externally defined groups - 100 < N < 1,000