To enable logging, open Designer and activate the configuration parameter "Common\Journal\LoginAudit". Once enabled, Identity Manager writes information in the system journal (table DialogJournal).
Login succeeded for module Active Directory user account, properties: , identity: username, client machine: MACHINENAME
The system writes this information into the DialogJournal table after a successful login.
If additional logging is required, a custom database trigger for INSERTs in DialogJournal will need to be created, but is not supported. Such a trigger can be used to write some additional information or fire another event.