http://docs.openstack.org/security-guide/content/ch025_web-dashboard.html seems to recommend against using ```signed_cookies``` and everything I find (for instance: http://stackoverflow.com/questions/12142058/performance-comparison-of-using-django-signed-cookie-session-over-django-db-ca) seems to indicate that ```cached_db``` is only an issue at very large scale. Which is not our case.

So we should keep the old one, imho.