From 0.2.20110529 and up, there is a privilege system for players.
The possible privileges are
In 0.4 the build privilege was changed to interact.
There is an option in the configuration file for setting the default privileges for new players.
default_privs = interact, shout
The player having the name in the “name” field of the configuration has all privileges. This makes the player in the local game able to do everything. The “name” field can also be used for setting the admin of the server. The extended privileges caused by this setting do not show up in /privs.
Privileges are stored in the new auth.txt file. The format of every line in that file is
name:hashed_password:privs
A real example:
celeron55:CcCUjNUDVJxmXmTHj+7WKHvA9Ds:build,shout
The auth.txt file is written periodically and at shutdown, so you should edit it only when the server is not running.