HTTP custom delivery

I'm trying to implement custom http delivery to our ticketing system (GLPI) to have tickets generated automatically if an alert comes up.

Connectivity has been set-up and calling a webservice which does not require authentication works fine. However, when authentication is required (and that is for 99% of the webservices) I'm not able to get this working.  I included the correct username & password in LM settings, ut keep getting the message "authentication failed".

It looks like I need to set authentication in some other way, but getting no clue what/how...

Anybody has this custom http delivery working?

Thanks,

Jeroen