Pull data from a REST API which has Authentication

Hi

New to PowerBI so please forgive me if query does not make complete sense!

I have PowerBI Desktop and want to get date from a REST web service.

The issue I have is the web service requires an authentication first, before I can call the methods for data I want.

The product is Traverse.

So, to logon I first have to issue command like;

http://hostname/api/rest/command/login?myusername/MyPassword

This authenticates me and returns success if logged on, I see in POSTMAN that a cookie is created for session.

Once I have done that I can call upon its many methods to pull data out, these are the methods I need access to for PowerBI

e.g.

http://hostname/api/rest/command/sla.status?slaSerial=2022436&calculationPeriod=Day&startTime=201803050000&endTime=201803081200&format=json

to get me json back with report data I want to pull into PowerBI to then produce charts and such

What I cannot see is a method to call the second URL without the authentication. The Get Data from Web source does not seem to accomodate this type.

Is there a way to do this with the Advanced Editor?

Thanks in advance