It works by using the Host of the request. When it receives something in
the form of: `<node>.<session>.play-with-docker.com` it does a reverse
proxy http request to `node`, validating that the `node` actually belongs
to the `session`.
If the node has a prefix `ip` and continues with a valid IP address
where the dots where replaces by underscores (like `ip10_0_0_1`) then it
will remove the `ip` prefix and and replace the underscores by dots, and
assume it is an ip address.
Add google recaptcha as an initial page before creating any session.
To configure recaptcha there are 2 environment variables that are needed
`GOOGLE_RECAPTCHA_SITE_KEY` and `GOOGLE_RECAPTCHA_SITE_SECRET`.
The code contains development defaults that should be set in production
to real values.
**NOTICE: Development defaults assume that the domain is `localhost`**
It fixes lots of bugs, can fallback to long polling, resize viewport of
terminals and share clients state of the session, so they all see the
same thing.
