如何修复C＃SSL / TLS验证

Question

我有一个简单的WebClient和FTP管理器。

我要从FTP服务器删除文件并上传，但已更新。 主要问题是The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel." "The remote certificate is invalid according to the validation procedure.

我尝试了论坛上的所有修复方法，但是没有用。

                    client.Credentials = new NetworkCredential("user", "password");
                    FtpWebRequest requestFileDelete = (FtpWebRequest)WebRequest.Create("ftp://(url)" + file);
                    requestFileDelete.Method = WebRequestMethods.Ftp.DeleteFile;
                    FtpWebResponse responseFileDelete = (FtpWebResponse)requestFileDelete.GetResponse();

                    client2.Credentials = new NetworkCredential("user", "password");
                    client2.UploadFile("ftp://(url)/log.log", Temppath2 + "/log.txt");
                    File.Delete(filepath);