How can we account for frequent username field changes in SFDC for the user sync in CPQ?

Summary:

Currently the SFDC username needs to be in sync with the Login field in Under User Integration in CPQ, we are trying to analyze if any other field from SFDC such as the federation ID can be used to replace the SFDC Username in CPQ.

We're experiencing frequent changes in the username field in SFDC for MR users and if this field isn't in sync with CPQ the integration fails, so if we can have a constant field from SFDC such as the federation ID in CPQ login field there's would be no need to sync as that field remains constant in SFDC.