Container Alias

Cross-account access via ACLs is possible today, but it's unpleasantly complicated, since we lack 3-rd party authentication. The Gerrit review #62494 contains an intriguing approach: add a so-called "container alias" feature, working across accounts. It allows existing clients to access containers made public (or permitted by ACL).

Unfortunately, implementation in middleware is intrinsicly deficient. It appears impossible to create an alias in a system like Swift race-free. Thus, replicators ought to take alias into account and reconcile conflicts with containers, if any. This requires moving the patch into the core, hence the blueprint.

See: https://review.openstack.org/62494