Typo. "user source" is the correct terminology. This is a classic feature of Ignition where all authentication and role assignments are performed by the Ignition gateway, with a number of backend technologies (internal, database, active directory) and some ability to chain.
"Identity Provider" is the modern feature of Ignition where authentication and roles are delegated to a web-based, standardized API. Ignition comes with its own identity provider implementation that points at any classic user source.
Ignition's user management tools rely on Ignition's control over users and roles through a classic user source. Standardized web authentication APIs do not expose user management.