Auth plugins provide a generic interface for authenticating requests.
The plugin name is specified using the '--auth-plugin' option, and
may either be the name of a class from `websockify.auth_plugins`,
or a fully qualified python path to the auth plugin class (see below).
An optional plugin parameter can be specified using the '--auth-source'
option (a value of `None` will be used if no '--auth-source' option is
specified).
Auth plugins should inherit from `websockify.auth_plugins.BasePlugin`,
and should implement the `authenticate(headers, target_host, target_port)`
method. The value of the '--auth-source' option is available as
`self.source`.
One plugin is currently included: `ExpectOrigin`. The `ExpectOrigin`
plugin checks that the 'Origin' header is an expected value. The list
of acceptable origins is passed using the plugin source, as a
space-separated list.
Solly Ross