By default sme does not work the way you are expecting or hoping.
ibay access rights are controlled by group membership ONLY for local access (LAN or VPN) but NOT for Internet web access.
You can have anonymous acess to ibays via web access.
If you want to protect ibays then password protect them for www or ftp access, in that case you logon with the username = ibayname and the password is the password that is set for the ibay if you enable password protection of the ibay.
Keep in mind that ftp is not secure and passes plain text passwords over the Internet, easily hacked.
If you want to control remote access to ibays according to usernames and group membership, then only enable local web access for the ibay, and get your users to establish a VPN connection to the server and then map drives to the ibay they are allowed to access.