http://arav.i2p/stuff/article/setting_up_a_tor_proxy_relay_hiddenserv
Of course, there are
many other options, e.g. client authentication. But in simple case all you need are those two options above. Every hidden service starts
with HiddenServiceDir <path> directory that contains public
and secret keys, hostname for a hidden service
and a directory called authorized_clients that stores info on all clients that are authorized to access this hidden service.