Make Application in RDP lose focus if RDP loses focus

Question

So i'am a software developer and working on an app that we host on Remote Desktops.
What i want to do is that if I (or the Customer) clicks out of RDP, the RDP will lose focus on their own personal system, but the application open inside the RDP will not lose focus.
Is there a way to make it work like if a person clicks out of RDP (RDP loses focus), the applications inside the RDP also loses focus. I can write a script or a service if i have to but i have no idea where to look or start. If you someone knows about a registry flag or knows something, can you please tell me.

Thanks.
Abdul Wasay.