Each of your frappe server is a separate service? Single Identity provider can provide userids to all your services. No need to create users on all services separately. Just Login via Frappe via the main Frappe IDP
I’ve not use this service.
In case of frappe, primary identity provider is one of your frappe server.
This server will host all your identities. OAuth 2 provider for Frappe Apps - #12 by revant_one