Upgrade to WKWebView causes API calls to fail: 401 Unauthorized

Due to Apple’s upcoming deprecation of UIWebView we are updating our Ionic mobile app to use WKWebView.

API calls to an MVC web application requiring authentication fail, returning 401 Unauthorized. These calls were successful using UIWebView. As WKWebView forces CORS, we are assuming the errors are caused by malformed CORS settings but have not found the root cause or solution. We have tried updating the CORS settings in the servers side API controllers, Global.asax, and web.config as well as the Ionic code.
We do have full control of both server and client side code. Has anyone in this forum experience with this type of setup?