When trying to connect remote clients to Cygwin/X, I get 'Authorization required, but no authorization protocol specified'

If you use VcXsrv, you should turn on "Disable access control" setting. But note, after that anyone from Network who has access to your X-server may show their UI on you X-server.

You need to install the xhost package from Cygwin and after starting the X server run the following:

DISPLAY=:0.0 xhost <remote_hostname_or_ip>