I can't get NSURLSession background tasks to use client certificates.
I have a simple app that creates an NSURLSessionDownloadTask from an NSURLSession that uses NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier(...).
I have a custom delegate that implements:
"func URLSession(session: NSURLSession, didReceiveChallenge challenge: NSURLAuthenticationChallenge, completionHandler: (NSURLSessionAuthChallengeDisposition, NSURLCredential?) -> Void)". For NSURLAuthenticationMethodServerTrust, I accept any server. For NSURLAuthenticationMethodClientCertificate, I have a hardcoded PKCS12 bundle with a single certificate and key from which I successfully create an NSURLCredential (using SecPKCS12Import), then pass that credential to the completion handler with .UseCredential.
At runtime, I get the didReceiveChallenge callback for ClientCertificate, then another for NSURLAuthenticationMethodServerTrust, then URLSessionDidFinishEventsForBackgroundURLSession right away without completing the TLS handshake.
If I change the NSURLSessionConfiguration to use NSURLSessionConfiguration.defaultSessionConfiguration(), the client cert is presented correctly and the download proceeds.
Both tests are done with the app in the foreground.
