Add SSL/TLS protocol support

DearFTP/Connection/Commands/CommandsDispatcher.cs

@@ -9,6 +9,7 @@ namespace DearFTP.Connection.Commands
     {
         public ICommand[] Commands { get; } = new ICommand[]
         {
+            new AuthCommand(),
             new ClntCommand(),
             new CwdCommand(),
             new DeleteCommand(),
@@ -21,6 +22,8 @@ namespace DearFTP.Connection.Commands
             new OptionsCommand(),
             new ParentDirectoryCommand(),
             new PassiveCommand(),
+            new ProtectionBufferSizeCommand(),
+            new ProtectionCommand(),
             new PwdCommand(),
             new QuitCommand(),
             new RenameCommand(),
@@ -43,15 +46,21 @@ namespace DearFTP.Connection.Commands
             }
 
             var commandExecutor = Commands.FirstOrDefault(x => x.Aliases.Contains(command, StringComparer.OrdinalIgnoreCase));
+            var stream = session.FtpStream;
 
             if (commandExecutor == null)
             {
-                session.FtpStream.Send(ResponseCode.NotImplemented, $"Command '{command}' not implemented or invalid");
-
+                stream.Send(ResponseCode.NotImplemented, $"Command '{command}' not implemented or invalid");
                 return;
             }
 
-            commandExecutor.Execute(session, session.FtpStream, command, argument);
+            if (session.Configuration.Tls.ForceTls && !session.IsTlsProtected && command.ToUpper() != "AUTH")
+            {
+                stream.Send(ResponseCode.InsufficientProtection, "Not protected connection is not allowed on this server.");
+                return;
+            }
+
+            commandExecutor.Execute(session, stream, command, argument);
         }
     }
 }