Comment 4 for bug 1631078

Frankly I didn't take too close a look at the code I added to cinder.context. I just needed something that gave me the current user's authenticated session and nicked the _ContextAuthPlugin(plugin.BaseAuthPlugin) class from nova.context, found it did what I needed it to do and used it. But from a closer look at keystoneauth1.access.service_catalog I suspect ServiceCatalogV3 wouldn't work due to incompatible token formats:

https://github.com/openstack/keystoneauth/blob/master/keystoneauth1/access/service_catalog.py#L240
https://github.com/openstack/keystoneauth/blob/master/keystoneauth1/access/service_catalog.py#L279

For some reason we appear to be getting a V2 token from the current user's session, otherwise ServiceCatalogV2 would not work.