The "Wiki Domain" is a concept added as part of Wiki@0.10 as part of providing a practical use of OAuth security.
It is the top of the domain/sub-domain tree of wiki that a wiki farm supports. Each wiki farm can support one, or more, wiki domains.
For example, if a wiki farm is serving `example.wiki`, and its sub-domains, the wiki domain is `example.wiki`.
The login dialog is currently served from the wiki domain.
A side-effect is that login is effected at the wiki domain, so the user will be known to all the wiki within that wiki domain.