Configuration/settings/public freebusy url
$c->public_freebusy_url = true;
in your configuration in order that anyone might access the freebusy information for any user. Only events marked as PRIVATE will be excluded from the report.
This applies to access via the /freebusy.php URL. Access to freebusy information via the scheduling extensions to CalDAV is not affected by this report.
Available from DAViCal version: 0.9.7.3 and later