Add invalidate doc string to identity plugin

This was simply copied and pasted from the abstract method it overrides.

Change-Id: Ica349e7302434be43e08fc272e8fce5699553d9a
Provide an __all__ for auth module

Define the public functions for the auth module. To access actual auth
plugins users should still be expected to pull in the right file but
this shows the interface most service will need.

Change-Id: If389c8c0e91166ca46c1766bf5b76ad9d66417b0
Merge "Add invalidate doc string to identity plugin"
Merge "Provide an __all__ for auth module"