Why Certificates?
The motivation behind PKI for inter-system communication is well made elsewhere (links). For the GB2 Final Grade Submission Enterprise Service, the motivation comes from the realization that the target endpoint for the grades submissions may be a service that is used by many different systems through out the Campus/Enterprise. Using PKI can simplify managing access to that endpoint service for both the client and the service provider administrators. And so by using x509 PKI for authz/authn, Gradebook2 should 'play well' in even the largest Campus infrastructures.