A GlobaliD Group can be 'Open', 'Closed' or 'Moderated', which has implications on who has the ability to join the Group.
An 'Open' Group is open for anyone to join.
A 'Closed' Group is invite-only, so in order to be admitted a member must receive an
invite from a Group owner or admin.
For a 'Moderated' Group, members can apply to join the group, but their membership application has to be approved by the group's owner before they become members.