Add Role Members

Adds one or more members (users and/or roles) to a role in a single atomic (all-or-nothing) batch. Idempotent — already-present members are accepted. Returns the requested members confirmed present.

Handling of a not-yet-provisioned member depends on the configured authorization backend: a backend that stores assignments itself accepts the member by id, whereas catalog-backed authorization requires the member to exist first and otherwise returns 404 — provision the user (via POST /user) or create the role before assigning. Behavior is consistent within a deployment.