Why
Grouper is a product in use by Yale for the management of ad-hoc groups. As of 8/11/17 the only thing that ServiceNow is using it for is Express Shipping.
How
Code
Grouper provides a REST interface. Typical operations are to check for group members, update/add to groups and to remove from groups. UPI is used as the key for a user and the group id depends on the group which you are managing. The groups for express shipping are here.
Authentication
Authentication is performed with basic auth with the s_servicenow account.
Troubleshooting
Grouper is routed through a mid server because it is not available publically like other services exposed through Layer 7 are. If the mid server is down, this service will not work. Simply make sure the mid server is up and this should function again.