I'd like to have our site invitation only, and when someone invites someone, they get a unique link that may only be used once. So after someone joins through that link, if they were to forward that link to someone else, it wouldn't work and would go to a page saying "sorry, this group is by invitation only" (or something like that).
I'm not sure if this matters, but it will also have the mobile side of things too, so I don't want anyone to be able to join via mobile either (unless invited through the one time invitation that expires)
Thanks =)