Admin accounts currently restrict a few operations, but leave all other operations completely open. Many use cases will require all operations to be authenticated. This can certainly be done by overriding the default_authentication_handler, but I think this very common use case can be handled in default_authentication_handler without increasing the complexity much.
Attached is a patch which adds a new config option, "require_valid_user", which restricts all operations to authenticated users only. Since CouchDB currently only has admins, this means that all operations are restricted to admins. In a future CouchDB where there are also normal users, the intention is that this would let them pass through as well.