Any GLPI CalDAV calendars is read-only for every authenticated user

Summary

GLPI stands for Gestionnaire Libre de Parc Informatique and it is a Free Asset and IT Management Software package, that provides ITIL Service Desk features, licenses tracking and software auditing. In GLPI before version 9.5.3, any authenticated user has read-only permissions to the planning of every other user, even admin ones. Steps to reproduce the behavior: 1. Create a new planning with 'eduardo.mozart' user (from 'IT' group that belongs to 'Super-admin') into it's personal planning at 'Assistance' > 'Planning'. 2. Copy the CalDAV url and use a CalDAV client (e.g. Thunderbird) to sync the planning with the provided URL. 3. Inform the username and password from any valid user (e.g. 'camila' from 'Proativa' group). 4. 'Camila' has read-only access to 'eduardo.mozart' personal planning. The same behavior happens to any group. E.g. 'Camila' has access to 'IT' group planning, even if she doesn't belong to this group and has a 'Self-service' profile permission). This issue is fixed in version 9.5.3. As a workaround, one can remove the `caldav.php` file to block access to CalDAV server.