If auditing of Login/Logout events is enabled for an Identity Manager environment, a list of users who have accessed the system can be obtained from the imsAuditEvent12 table of the IM object store. For example, on MS-SQL, a query like the following will provide a list of users who have successfully accessed the system:
SELECT * FROM imsAuditEvent12 where event_name = 'Login' and event_state = 'completed'
Unsuccessful Login attempts can be shown with a query such as:
SELECT * FROM imsAuditEvent12 where event_name = 'Login' and event_state = 'invalid'
The admin_name column of that table shows the user's login ID.