Corkscrew

   I work in a place where I have no direct access to the outside world in a way other than HTTP (through an authenticated proxy) and email. However sometimes I need to access the external world, usually through SSH to pick some external resources, push GIT repository or so. And this is not a problem with PuTTY for it has a variety proxies build-in:

   But while working on my Linux running on Oracle VirtualBox I have to rely on pure OpenSSH only. And there is no HTTP proxy support in OpenSSH just out of the box. And there is a solution for OpenSSH as well - this is Corkscrew, a small utility but it does the work and supports HTTP authentication even!

For github.com purpose I use following config in the file ~/.ssh/config:

Host github.com
  ProxyCommand corkscrew proxy.acme.com 80 %h %p ~/.ssh/proxyauth
  ServerAliveInterval 60

In the ssh config above the clause "Host github.com" means the configuration applies only for the target like ssh git@github.com. And this is exactly what git is doing when pushing to a github repository. It pushes through ssh. Following clause "ProxyCommand corkscrew [...]" means ssh has to run corkscrew commands with the following arguments. Here you have the simplest corkscrew syntax:

$ corkscrew -h
corkscrew 2.0 (agroman@agroman.net)
usage: corkscrew <proxyhost> <proxyport> <desthost> <destport> [authfile]
$

First two arguments identify the proxy and its port Proxy.acme.com 80. The target hostname and the port is delivered by ssh itself through variables %h and %p. The last argument is the auth file - if you need credentials for your proxy, create a file, insert the username:password inside (just one line) and your connection through proxy will be authenticated. Usually you don't need it.
The extra line with ServerAliveInterval is useful when I have an idle interactive ssh connection. You can safely remove it from github.com configuration.

That's it! Try it out.

Links

1. Corkscrew homepage.
2. Corkscrew, how to setup.