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The Auth System
The auth system for Swift is based on the auth system from an existing architecture -- actually from a few existing auth systems -- and is therefore a bit disjointed. The distilled points about it are:
- The authentication/authorization part is outside Swift itself
- The user of Swift passes in an auth token with each request
- Swift validates each token with the external auth system and caches the result
- The token does not change from request to request, but does expire
The token can be passed into Swift using the X-Auth-Token or the X-Storage-Token header. Both have the same format: just a simple string representing the token. Some external systems use UUID tokens, some an MD5 hash of something unique, some use "something else" but the salient point is that the token is a string which can be sent as-is back to the auth system for validation.
The validation call is, for historical reasons, an XMLRPC call. There are two types of auth systems, type 0 and type 1. With type 0, the XMLRPC call is given the token and the Swift account name (also known as the account hash because it's usually of the format <reseller>_<hash>). With type 1, the call is given the container name and HTTP method as well as the token and account hash. Both types are also given a service login and password recorded in Swift's resellers.conf. For a valid token, both auth system types respond with a session TTL and overall expiration in seconds from now. Swift does not honor the session TTL but will cache the token up to the expiration time. Tokens can be purged through a call to Swift's services server.
How the user gets the token to use with Swift is up to the reseller software itself. For instance, with Cloud Files the user has a starting URL to an auth system. The user starts a session by sending a ReST request to that auth system to receive the auth token, a URL to the Swift system, and a URL to the CDN system.
History and Future
What's established in Swift for authentication/authorization has history from before Swift, so that won't be recorded here. It was minimally integrated with Swift to meet project deadlines, but in the near future Swift should have a pluggable auth/reseller system to support the above as well as other architectures.