Run the echo service.
The echo service can be run on port 8000 by executing the following:
$ python -m keystonemiddleware.echo
When the auth_token module authenticates a request, the echo service will respond with all the environment variables presented to it by this module.
Bases: object
Runs an instance of the echo app on init.
A WSGI application that echoes the CGI environment back to the user.