Blocking proxies

[DuckTales]

Hi guys,

To reduce spam and for business reasons, we've decided to restrict the
number of web-proxy who access our site. Previously, on apache, we used
this technique(see below) and later switched to blockscript to restrict
users.

http://perishablepress.com/press/2008/04/20/how-to-block-proxy-servers-via-htaccess/

I'm curious to understand how the apache rules can be translated into
nginx compatible format. Any assistance would be greatly appreciated!
Thanks a lot.

Doug

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,163611,163611#msg-163611