Alpaca is an HTTP/HTTPS proxy. It is designed for users of Unix tools, who operate inside networks that use proxy auto-configuration (PAC) files and require NTLM authentication.

It currently does not yet implement many important features, such as SOCKS, HTTP/2, and many of the predefined JS functions that PAC files use. Contributions are welcome, please reach out to me if you'd like to help!

To download and install Alpaca, use:

$ go get -v -u github.com/samuong/alpaca

Then start Alpaca by running the alpaca binary.

If your proxy requires NTLM authentication, you'll need to supply your domain and username (via command-line flags) and a password (via a prompt):

$ alpaca -d MYDOMAIN -u me
Password (for MYDOMAIN\me):

If you're using macOS or GNOME 3+, Alpaca will be able to find the PAC URL from your system proxy settings. You can also set the URL manually using the -C flag. If no PAC URL is found, Alpaca will act as a direct proxy (i.e. a non-caching proxy, without a parent proxy).

You can then configure your tools to send requests via Alpaca. Usually this will require setting the http_proxy and https_proxy environment variables:

$ http_proxy=localhost:3128
$ https_proxy=localhost:3128
$ export http_proxy https_proxy
$ curl -s https://raw.githubusercontent.com/samuong/alpaca/master/README.md
# Alpaca
...

When moving from, say, a corporate network to a public WiFi network (or vice-versa), the proxies listed in the PAC script might become unreachable. When this happens, Alpaca will temporarily bypass the parent proxy and send requests directly, so there's no need to manually unset/re-set http_proxy and https_proxy as you move between networks.