How to check if a client can use windows authentication
You want to check AUTHENTICATION_TYPE in the DBA_USERS view. Users who are authenticated externally (EXTERNAL in the view), are authenticated by the operating system. A user cannot be both internally and externally authenticated, or be altered to switch authentication methods once created. If you haven't deliberately created externally authenticated users, then you won't have a problem.
See here: https://docs.oracle.com/en/database/oracle/oracle-database/18/ntqrf/overview-of-manually-administering-external-users-and-roles.html#GUID-8A209E30-4BA9-4993-80F5-AF0A82ADEB5B