Thank you for the reply.
Could you point me to the document to understand OAuth2 authentication using system account, without manual intervention?
Also, I found that the system authentication is only available for sandbox, is it still available only for sandbox?.
I read at
https://fhir.cerner.com/millennium/r4/- "Each resource interaction documents the type of authentication acceptable (patient, provider, and/or system). While an interaction may list system authentication, this is currently available only in sandbox for beta testing and is not available in production yet."