You may add a user to the TiddlyWeb store from the command line using the twanager adduser command. See user and Auth Model for information on why you may want to. To create the user {{{barney}}} with password {{{dinosaur}}} and no roles:

{{{ twanager adduser barney dinosaur }}}

The plugin {{{tiddlywebplugins.socialusers}}} provides HTTP access to managing users.

See also: How do I give a user a role? How do I create or update a User object in code?