This will probably not answer your question directly, but there's usually no need to do that. The only benefit of having authorised user in Activiti is that you have variables like "initiator" populated automatically - apart from that there is no direct link between Activiti users/groups and task (potential) assignees. We are using generic login to secure REST services and then simply assign tasks to the SSO (Google App Engine) user IDs even though there are no associated records in ACT_ID_USER, ACT_ID_GROUP or ACT_ID_MEMBERSHIP tables.