External service - need to contant local machine

I'm having a web application under IIS which runs in production and available globally. Let it be "app A". Currently - it's needed to add one more service - let's call it "app B". App B should send GET request to App A which will return specific item for further processing by App B. App A should know nothing about App B at all.

Well, when both web apps are deployed globally and have IPs or CNAMEs - all is clear.

What I need is ability to work with App B from local setup of App A (e.g. from local DEV machine). Such machine is behind the NAT and has restrictions by many policies. Also if there are more than one developer in the team - it will be hard to serve all them with such security.

Though about kind of proxy solution. Can you propose something that's on top of your mind?

Thanks in advance.

p.s. Local setup of App B is a bad approach as well.