Limit file types that can be proxied

[reference123]

I am trying to limit the file types that can be proxied from our backend server.  I am trying to limit it to jpg, gif, png, css and then two other specific files  - Thumbnail.ashx and hearbeat.htm.  I am also hoping to limit access to only certain referers.

I have tried this code which works fine for the jpg, gif, png, css but is not working for the heartbeat.htm file.  It gives a 404 on all .htm files including heartbeat.htm.

location ~* (\.jpg|\.png|\.gif|\.css|ThumbNail\.ashx|heartbeat\.htm)$ {

		valid_referers 
			none			
			blocked
			example.com 
			www.example.com
			examplellimages.com
			www.examplellimages.com
			1.examplellimages.com
			2.examplellimages.com
			3.examplellimages.com
			4.examplellimages.com;
		
		if ($invalid_referer) {
			return 404;
		}


	
		proxy_pass	http://exampleimages_com;
    }

Any help would be appreciated.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,91106,91106#msg-91106