adding caldav/carddav next to dovecot

[Marc]

> 
> we are using Sabre DAV. Very stable and its performance depends on the
> performance of your webserver.

If I may ask, what average rate of requests per second per 1000 users do you have?

> We are using Apache-MPM prefork. If your webserver can handle HTTP-
> requests for 10k users, it will handle CARDDAV/CALDAV-requests for that
> amount of users as well.

I was thinking of putting a container behind a proxy (and ideally autoscalling instances) so support for the proxy-protocol would be nice. 

> If you are familiar with php-programming, you may extend Sabre DAV.
> Standard Sabre DAV has its own user database. We extended the SabreDAV
> authentication mechanism such that user-credentials are pulled from the
> same database that Dovecot is using.
>

I would prefer ldap