Pluggable Authentication

Status
In release 0.5.0 a framework has been implemented which allows a hook to provide the authentication and user information. This does not allow for anything other than providing authentication and user data at this stage. Notably there is currently no ability for an external source to provide relationship information although any implementation of an authentication hook could take the opportunity to reflect remotely accessible relationships into local DAViCal tables during the authentication phase.

The Goal
The goal of pluggable authentication is to enable the use of external systems as sources of data for authenticating users connecting to DAViCal.

An other secondary goal would be to support having the external source also provide the relationship information used by DAViCal to control permissions between users. See ExternalRelationshipInfo for plans around the delegated relationships coming from an external data source.

The Plan
Implement a hook in the login process.

Limitations
At this point the planned system will not meet the secondary goal. To meet the secondary goal would require some recoding of those functions which calculate permissions to use library functions, which would also need to be written.

A suggested Authentication source
Webauth authentication would be good. AIUI it just passes a set of Apache environment variables after the authentication process to specify which user has logged in, so I'd think it'd be fairly easy to implement. Hm, I guess you'd need to dynamically create non-existent users as they were authenticated. But that wouldn't be too hard, would it?
 * It has to be done anyway, and is in fact done already in the existing external authentication plugin.

The same would allow to authenticate based on an SSL client certificate. The CN could be used as username, and password should never be checked. Something like that.