You can use this as a simple authentication mechanism.
Rather than have to login with a username & password, you can specify a ProxyKey that must be passed from a client before requests are processed.
This is helpful in situations where you would like to authenticate and execute an action in a single step.

Specify a server to which to send your commands (x.x.x.x or hostname).
This should match the server name specified in your config file's "host" entry. If you do not specify a server, the proxy will pick the first one it finds -- fine in single-server configurations.