Section
2.1.3
Top Level
General
Do not require users to log in multiple times when accessing a set of interrelated sites. Provide a mechanism so their session cookie will be valid across all these sites and they won't have to log in again.
Django

A single Django instance can serve multiple sites, but Django's authentication system relies on session cookies, which are tied to a domain. In order to share a session cookie across multiple sites, those sites must be subdomains of a common domain. Note that you will need to set theSESSION_COOKIE_DOMAIN setting accordingly.

Natural Webagent
Use EID authentication only. Don't create your own authentication system.