[tzury]

I have only control on the web app, not the clients.

It is posted on SO in parallel, but there is no help at there, so I thought to try my luck in this community.

[manuscreationis]

Might be able to do UserAgent parsing then... since you're doing a very specific target, it might (keyword might) be simple to do a string compare against whatever the UserAgent of the WinForm app is (I have no idea what it would be, but you could test this very easily), and use that as how you detect.