How do I show 403 error

[blason]

Hi Guys,

I just setup nginx reverse proxy for my webservers which has port 80/443
opened from internet and have very restircted access on firewall to the
destination servers again those to particular servers on port 80 and 443.

What I see in the logs is 
"GET http://www.baidu.com/ HTTP/1.1" 200 626 "-" "Mozilla/4.0 (compatible;
MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727; .NET CLR 3.0.04506.648;
.NET CLR 3.5.21022)" "-"

I know people are trying to use my server as open proxy which is failing and
even I am not able to browse the sites but I am not getting any error page
on my browser and just see blank page that means server is accepting the
request but unable to forward. 

Hence would like to know how do I throw error message in nginx so that those
requests would not even accepted by my proxy.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,257041,257041#msg-257041