HMAC based auth handler

[codegangsta]

from @nimajalali

I'm finalizing a HMAC based auth handler. Using Amazon S3 signed and authorized model, more info here.

I use it for server to server communication where a pre shared secret is possible. The handler adds to the S3 model by enabling the use of a nonce.

Should this be under the auth package, possibly auth.HMAC? If so how should I go about adding info to the auth README?

Also, any thoughts on how to incorporate multiple auth handlers? For instance I have API endpoints that are accessed from servers as well as clients. I use this HMAC auth handler to handle server to server auth and another handler for session based auth. Today I have to create two separate endpoints to enable auth from either handler.