User accounts are a part of the user.openshift.io group. The kinds available are
groups / group
identities / identity
users / user
useridentitymappings / useridentitymapping
Users have identities mapped directly on the user CR. The useridentitymapping CR seems to be just API related.
$ oc get groups -ojson | jq -r '.items[] | select(.users | index("OPENSHIFT USERNAME"))'