Partial obfuscation in Splunk Cloud

[Flobzh]

Hello experts,

I'm trying to obfuscate the UserName and ComputerName from my events before indexation, while keeping the possibility of using the data to group from a common source.

Configuration: data are pushed by a UniversalForwarder (no transform options) to a SplunkCloud instance (limited setup).

Example:

I have this:

time1|UserName=user1|ComputerName=FR1234|EventStart
time2|UserName=user1|ComputerName=FR1234|EventEnd
time3|UserName=user2|ComputerName=US4321|EventStart
time4|UserName=user2|ComputerName=US4321|EventEnd
time5|UserName=user1|ComputerName=US4321|EventStart
time6|UserName=user1|ComputerName=US4321|EventEnd

And want something like this:

time1|UserName=#####|ComputerName=FR#|GeneratedSessionID=eifiweuh|EventStart
time2|UserName=#####|ComputerName=FR#|GeneratedSessionID=eifiweuh|EventEnd
time3|UserName=#####|ComputerName=US#|GeneratedSessionID=fwefwe|EventStart
time4|UserName=#####|ComputerName=US#|GeneratedSessionID=fwefwe|EventEnd
time5|UserName=#####|ComputerName=US#|GeneratedSessionID=hkukuyy|EventStart
time6|UserName=#####|ComputerName=US#|GeneratedSessionID=hkukuyy|EventEnd

Where GeneratedSessionID=function(user1,FR1234,encryptKey) or something similar. Meaning that the same couple computer+user will always create the same GeneratedSessionID

I'm looking at adding a SECCMD setting on the Advanced tab of my SourceType. I see how to anonymize the UserName and ComputerName, but not how to add a new field based on the others. 

Any advise in that direction would be welcome, or any solution that will match with the restriction of my configuration.

Thanks in advance

Florent