I should be able to define a Shared Link that *requires* membership

(User Story, Closed -> Fixed, Priority: Critical, Test Status: No automated tests yet , Reported By Bad Link: Thing 3y285jl not found, )
Invites
Summary: Currently, a Shared Link always allows you to enter as a Guest. But for the Arisia Space (and really, many others), you want to require that people sign up first.
Hopefully this doesn't require doing too much damage to Shared Links.