Update to this: When trying to do this on a physical device rather than a simulator, I get a pop up that says: Proxy Authentication Required Enter the password for the HTTP proxy [proxy url] in Settings. After opening the Settings app and entering the username and password, the proxy works as expected on the web view. Unfortunately this doesn't particularly help my use case. Hopefully this is intended to be able to be done using applyCredential.

I've got the same problem, specifically with a HTTP proxy. Without authentication I can use the proxy fine, but when authentication is enabled I get the error: The operation couldn’t be completed. Authentication error in the didFailProvisionalNavigation WKNavigationDelegate function.