I have been asking around on the calibre forums about LDAP/AD authentication. (Open)LDAP or ActiveDirectory authentication - MobileRead Forums
The answer to my question:
Use a reverse proxy, then you can use whatever authentication scheme you like in the proxy server. The calibre server uses http auth set it to use basic http uath instead of digest and pass the Authorization header from the proxy server to the calibre server.
Would this be an option/possible to implement in NS? And would this be an option for other NON LDAP/AD applications to configure authentication? (like Gibbon for instance)