How to create a unfied auditing policy that captures logons from privileged users

By default, only unsuccessful logon attempts are audited by mandatory auditing under Unified Auditing.
The policy used for this purpose is ORA_LOGON_FAILURES, and it will audit both privileged and non-privileged users' attempts to logon to the database.

If you want to audit all privileged users that have successfully logged onto the database, you need to create a new policy.

Here is how:

 CREATE AUDIT POLICY PRIVILEGED_USER_LOGONS
   ACTIONS  LOGON
   WHEN 'SYS_CONTEXT (''USERENV'',''CURRENT_USER'') IN (''SYS'',''SYSTEM'')'
   EVALUATE PER SESSION; 

Start using it:

AUDIT POLICY PRIVILEGED_USER_LOGONS;

The resulting audit record can be found immediately afterwards, with this query against UNIFIED_AUDIT_TRAIL:

select os_username "os user",
       userhost "host",
       authentication_type "authtype",
       dbusername "db user",
       client_program_name "client",
       event_timestamp "time",
       action_name "action",
       system_privilege_used "sys priv",
       unified_audit_policies "aud pol"
from UNIFIED_AUDIT_TRAIL 
where event_Timestamp = (select max(event_Timestamp) from UNIFIED_AUDIT_TRAIL)
order by event_timestamp desc;

Result:

os user	host	authtype	db user	client	time	action	sys priv	aud pol
oracle	myserver.mydomain.com	(TYPE=(OS));(CLIENT ADDRESS=((PROTOCOL=beq)(HOST=192.168.0.34)));	SYS	sqlplus@myserver.mydomain.com (TNS V1-V3)	10.03.2022 11:38:14,972147	LOGON	SYSDBA	PRIVILEGED_USER_LOGONS