Cloned from launchpad blueprint https://blueprints.launchpad.net/python-keystoneclient/+spec/auth-plugins.

Description:

Nova and other clients have the concept of a basic connection class that provides authorization and then can be shared amongst all clients. This provides many benefits including http sessions, easily sharing tokens between clients, caching etc. 

We should do this in keystoneclient so that we can be in control of the session class for adding things like kerberos when they are required. 

This is essentially the same as https://blueprints.launchpad.net/python-keystoneclient/+spec/keystoneclient-auth-system except we are currently just concerned with the architecture.

Specification URL (additional information):

https://etherpad.openstack.org/keystoneclient-auth-system