You need to have History=1 in the [SECURITY] section of your Enterprise Server JDE.INI that your web server is authenticating against. It will then log all user sign on and sign offs in the F9312 table , you can view this from the P98OWSEC application and take the Security History form exit.
Enabling this setting will cause this table to grow over time if you have a large number of users and /or batch job volume. So enable this with caution and take necessary measures to purge this table periodically if needed.
