multipart / form-data upload任务不会为iOS中的大文件调用Authentication Challenge

Question

我正在尝试使用URLSession.dataTask(with: r as URLRequest)将zip文件从移动设备上传到远程Azure服务器。为此，我使用NSURLAuthenticationMethodServerTrust和NSURLAuthenticationMethodClientCertificate身份验证。当zip文件的大小为~15KB时，两者工作正常。

但对于更大的文件，我只看到NSURLAuthenticationMethodServerTrust然后请求超时。我已经花了3天没有任何具体方向。

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

    if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodClientCertificate{
        if useFirstCert, let certURL = Bundle.main.url(forResource: "azure-client1-cert", withExtension: "p12"){
            let cred = credential(from: certURL, password: "passcode")
            completionHandler(URLSession.AuthChallengeDisposition.useCredential, cred)
        }else {
            completionHandler(URLSession.AuthChallengeDisposition.cancelAuthenticationChallenge, nil)
        }
    }else if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust{
        completionHandler(URLSession.AuthChallengeDisposition.rejectProtectionSpace, nil)
    }else{
        completionHandler(URLSession.AuthChallengeDisposition.performDefaultHandling, nil);
    }
}