There is not currently any built-in functionality to sync users from an OIDC provider.
Your best bet right now would be to build your own small script or service. For example, you could periodically poll for users in both Central and Keycloak and align the two lists. Alternately, you could use an event-based approach using https://github.com/p2-inc/keycloak-events and ideas from Webhooks in ODK Central - #16 by spwoodcock