PAC (Proxy Auto-Configuration)

A Proxy Auto-Configuration (PAC) file is a script used by web browsers and other user agents to automatically determine whether to send web traffic directly to the destination server or via a proxy server.

PAC files contain JavaScript code that defines a FindProxyForURL function. This function takes a URL and host as input and returns a string specifying the proxy server to use, or indicates that the connection should be made directly.

Example (JavaScript):

Here is an example of a PAC file:

function FindProxyForURL(url, host) {
  // If the URL matches "example.com", use the specified proxy server
  if (shExpMatch(host, "*.example.com")) {
    return "PROXY proxy.example.com:8080";
  }

  // If the URL matches "internal.local", connect directly
  if (shExpMatch(host, "*.internal.local")) {
    return "DIRECT";
  }

  // For all other URLs, use another proxy server
  return "PROXY another-proxy.com:8080";
}

In this example:

• Requests to any subdomain of example.com are routed through proxy.example.com:8080.
• Requests to any subdomain of internal.local are connected directly.
• All other requests are routed through another-proxy.com:8080.