I make cross-origin ajax calls with php and I want to accept only requests from Overwolf

I’m working with PHP and I have a question. I make cross-origin ajax calls with PHP and I want to accept only requests from Overwolf. (and not the other servers).
What should I modify in my headers?

To not tied to one specific APP, check for the User-Agent in the API request from Overwolf application to your server, and decide if to process the request or discard it.

If it contains “OverwolfClient” as a user agent - it means that the request come from your Overwolf app.

The request should look like this: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36 OverwolfClient/0.134.0.26