Shared Auth Session

To be really stateless, we need a mecanism to share the auth session between nodes.

• we probably need to build some kind of shared auth session with a common persistence backend
• we can probably reuse some of the code from IDM and use ElasticCache as a shared session backend
• https://github.com/nuxeo/nuxeo-idm/tree/master/nuxeo-idm-auth/src/main/java/org/nuxeo/idm/session