We have an interface to add/remove users to/from permission groups, see details:
http://nabble-support.1.n2.nabble.com/API-for-Nabble-2-tp792099p5571255.htmlBut the forum administrator cannot register a user and provide an email and password for him/her. The user must register by himself. So the interface above is useful when you have a private forum in your site and you must add users to the group that has access to the forum. Even if the user hasn't registered yet, you can use that interface to add his account to the group, but he will have to finish the forum registration to have this access.