Implement a short term in memory auth cache.
Merge branch 'master' into caching-authenticator
Fix waiting, and error propagation.
Fix lint.
Actually define an interface for token acquisition.
Use a different dummy return value to prevent accidental success with the default return values.
Inch closer to the exarkunic ideal of 1 assertion per test.
Merge pull request #271 from rackerlabs/caching-authenticator

Caching authenticator (ready for review)