string sourcePath = "C:\\Xie\\Test\\";
            string siteUrl = "https://xxx.sharepoint.com/sites/test";
            var authManager = new OfficeDevPnP.Core.AuthenticationManager();
            // This method calls a pop up window with the login page and it also prompts 
            // for the multi factor authentication code. 
            ClientContext ctx = authManager.GetWebLoginClientContext(siteUrl);
            // The obtained ClientContext object can be used to connect to the SharePoint site. 
            Web web = ctx.Web;
            ctx.Load(web, w => w.Title);
            ctx.ExecuteQuery();
            Console.WriteLine("You have connected to {0} site, with Multi Factor Authentication enabled!!", web.Title);

            List targetList = ctx.Web.Lists.GetByTitle("TestFolder");

            FolderCollection oFolderCollection = targetList.RootFolder.Folders;

            ctx.Load(oFolderCollection);
            ctx.ExecuteQuery();

            foreach (Folder oFolder in oFolderCollection)
            {
                Console.WriteLine("Folder Name: " + oFolder.Name + " Folder URL: " + oFolder.ServerRelativeUrl);

                Folder folder = web.GetFolderByServerRelativeUrl(oFolder.ServerRelativeUrl);
                ctx.Load(folder);

                DirectoryInfo directory = new DirectoryInfo(sourcePath);
                FileInfo[] files = directory.GetFiles("*.*");
                foreach (FileInfo file in files)
                {
                    var filePath = sourcePath + file.Name;
                    FileCreationInformation newFile = new FileCreationInformation();
                    newFile.Content = System.IO.File.ReadAllBytes(sourcePath + file.Name);
                    newFile.Url = file.Name;
                    newFile.Overwrite = true;
                    Microsoft.SharePoint.Client.File newspFile = folder.Files.Add(newFile);
                }
                ctx.ExecuteQuery();
            }

            Console.ReadLine();