DispatchQueue.global(qos: DispatchQoS.QoSClass.default).async(execute: {

            let taskID = self.beginBackgroundUpdateTask()
            print("background taks started:")
            print(taskID)

            if let userusername: String = Keychain(service: KCservice, accessGroup: KCaccessGroup).accessibility(.afterFirstUnlock)["userusername"] {
                if userusername != ""{
                    if let userpassword: String = Keychain(service: KCservice, accessGroup: KCaccessGroup).accessibility(.afterFirstUnlock)["userpassword"] {
                        if userpassword != ""{

                            let loginString = String(format: "%@:%@", userusername, userpassword)
                            let loginData = loginString.data(using: String.Encoding.utf8)!
                            let base64LoginString = loginData.base64EncodedString()

                            let url = URL(string: "\(polyserver)oauth/v2/user/tokens")
                            let postParams: [String : Any] = [:]

                            var request = URLRequest(url: url!)
                            request.httpMethod = "DELETE"
                            request.setValue("application/json", forHTTPHeaderField: "Content-Type")
                            request.setValue("basic \(base64LoginString)", forHTTPHeaderField: "Authorization")
                            request.setValue("no-cache", forHTTPHeaderField: "Cache-Control")
                            do
                            {
                                request.httpBody = try JSONSerialization.data(withJSONObject: postParams, options: JSONSerialization.WritingOptions())
                            }
                            catch
                            {
                                print("Caught an error: \(error)")
                            }
                            let task = URLSession.shared.dataTask(with: request as URLRequest) { data, response, error in
                                guard error == nil && data != nil else {                                                          // check for fundamental networking error
                                    print("error=\(String(describing: error))")
                                    self.endBackgroundUpdateTask(taskID)
                                    return
                                }

                                if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {           // check for http errors
                                    print("statusCode should be 200, but is \(httpStatus.statusCode)")
                                    print("response = \(String(describing: response))")
                                    self.endBackgroundUpdateTask(taskID)
                                    return
                                }

                                let responseString = String(data: data!, encoding: String.Encoding.utf8)
                                print("responseString = \(String(describing: responseString))")
                                self.endBackgroundUpdateTask(taskID)


                            }
                            task.resume()



                        }else{self.endBackgroundUpdateTask(taskID)}
                    }else{self.endBackgroundUpdateTask(taskID)}
                }else{self.endBackgroundUpdateTask(taskID)}
            }else{self.endBackgroundUpdateTask(taskID)}


        })

    }