Thread:Extension talk:OpenID/OpenID with Google Apps/reply (5)

At Special:ListGroupRights, you can see that all users have the "createaccount" permission, which allows anyone to create an account. What you want is presumably to change the default permissions so that only administrators have the "createaccount" permission. See Manual:User rights for details. If only the administrator can create an account, then the administrator has to go to Special:CreateAccount to create all accounts and then hand over the login credentials to the person who is going to use the account.