There are a couple routes to go from here. My recommendation would be to create a lookup of the user accounts, this should include AD username, email address, first and last name, and/or some unique identifier of the user. This lookup can be manual or automated (recommend automating through ldap/AD integration with Splunk). Once the lookup is configured, integrate your log sources that will identify authentication activity (Windows, O365, VPN,etc). Validate the log sources are parsing the fields correctly and compliant to the CIM standards. Once validated, add those indexes of log sources into the Authentication datamodel, then use your SPL to identify your requested criteria. Example search below:
|tstats `summariesonly` values(Authentication.app) as app values(Authentication.action)
from datamodel=Authentication.Authentication
where [inputlookup terminated_users.csv |fields user |rename user as Authentication.user]
by _time, Authentication.src, Authentication.user
|`drop_dm_object_name(Authentication)`
... View more