Several people out there are reporting this as a bug. I am not sure it is.
I am using iOS 9.3, Xcode 7.3
Previously, I was using UIWebView to access a log in page (we use shibboleth), which stored the authentication cookies in NSHTTPCookieStorage.sharedHTTPCookieStorage()
Using UIWebView, this played nicely with NSURLSession when accessing web services as they shared the same cookie storage.
I have now tried switching to MKWebView as suggested in the documentation, and this process no longer seems to work. I can only assume cookie storage is sandboxed.
Is there a documented way to share cookies between MKWebView and NSURLSession?