Users actually all get their own txt file in the users folder. You can of course chose to generate these yourself.
Every file in the users folder is an SHA-512 hash of the user name (lowercased) followed by
`.txt`. The contents of the file should be the user’s password added to the back of the user name hash, and then again hashed with SHA-512.
Example code that creates a new user is here: https://github.com/Kroc/NoNonsenseForum/blob/e8a996c6cd3eb97c9de8762e3aa31b3b29508f93/start.php#L189-L198