Authenticating from azure kubernetes function app to on prem windows server

I am new, not sure where to post this but it sounds similiar to the original poster here. I am trying to figure out how to get a azure based kubernetes function app to authenticate with our on premise windows IIS server, preferably using windows authentication. The kubernetes cluster can “see” the on prem server via a azure express route. How can I make this work?

No one knowledgeable in here?