The Proxy Auto-Configuration URL

05 January 2013

One of the easiest ways to change your ip address with a proxy server is by using a proxy auto-configuration url in your web browser. A proxy auto-configuration url tells your browser when to use a proxy server, and what proxy server hostname and port to use.

How does a Proxy Autoconfiguration URL Work?

A proxy auto-configuration url instructs your web browser to download a javascript PAC file, normally called proxy.pac, which contains at least one javascript function called FindProxyForURL. Most of the time, this function simply tells your browser to always use a specific proxy server hostname and port for all requests. But the function can also restrict proxy usage based on the request. For example, a proxy server might only support http requests, but not https requests. In that case, the function would examine the request, and if it's for a https url, it would tell the browser to skip the proxy and go directly to the site. However, if the request is for a normal http url, then the proxy would be used. ProxyMesh supports both http requests and https requests through its anonymous proxy server, and so its proxy.pac auto-configuration function will work as both a http proxy server and a https proxy server, but will ignore any non-http requests.

How do I use a Proxy Auto-Config URL with an Authenticated Proxy Server?

Because proxy auto-configuration urls do not support specifying proxy usernames and password (and for good reason, because it would be a security risk), you must use IP address authentication. ProxyMesh supports address IP authentication for its rotating proxy server, which you can configure after you signup for ProxyMesh. Once your IP is registered with the proxy server, then the proxy auto-config will handle the rest, by specifying the proxy server hostname and port for each request.

How do I setup Automatic Proxy Configuration?

First, you need to have a proxy auto-config url to use. ProxyMesh provides all subscribers with this url in the account dashboard, which you can find after you signup for ProxyMesh.

Once you have a url to auto-config the proxy, you must go into your browser's proxy or network settings and look for Automatic proxy configuration, Autoconfiguration url, Automatic proxy configuration url, or PAC File URL, and copy/paste the url. Once you save this url in the settings, your browser will be using the automatic proxy configuration for all future requests.