Hello.

Currently, this functionality is not provided out-of-the-box, however it is easy to implement it. It depends on what do you mean by “un-register” – whether to delete user, or disable her. Both options are possible via API and you can find code examples below.

Delete current user:

CMS.SiteProvider.UserInfoProvider.DeleteUser(CMS.CMSHelper.CMSContext.CurrentUser.UserName);

Disable user:

using CMS.SiteProvider;
 
// Get UserInfo of the specified name
UserInfo user = CMS.SiteProvider.UserInfoProvider.GetUserInfo("Alice");
 
if (user != null)
{
  // Disable user
  user.Enabled = false;
}

Best Regards,
Radek Macalik