func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {

    guard challenge.previousFailureCount == 0 else {
        print("too many failures")
        challenge.sender?.cancel(challenge)
        completionHandler(.cancelAuthenticationChallenge, nil)
        return
    }

    guard challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodNTLM else {
        print("unknown authentication method (challenge.protectionSpace.authenticationMethod)")
        challenge.sender?.cancel(challenge)
        completionHandler(.cancelAuthenticationChallenge, nil)
        return
    }

    guard self.doesHaveCredentials() else {
        challenge.sender?.cancel(challenge)
        completionHandler(.cancelAuthenticationChallenge, nil)
        DispatchQueue.main.async {
            print("Userdata not set")
        };
        return
    }

    let credentials = URLCredential(user: self.username!, password: self.password!, persistence: .forSession)
    challenge.sender?.use(credentials, for: challenge)
    completionHandler(.useCredential, credentials)
}