Both 2 and 3 the answers are no, it is not possible.
Please note that if you want to submit Analytics Events using authenticated user this is very easy; simply switch to the MIP SDK methods as shown in the Analytics Event Trigger via MIP .Net library sample.
Analytics Event Trigger via XML uses the Event Server port 9090 and no authentication.
Thank you, I followed your advice in (1) - it’s exactly what I need.
Regarding other questions… I need to protect port 9090 from spoofing XML messages. So the MessageCommunication method does not solve the problem at all…