Right now calendar/export_execute.php is simply dying on various controlled situations:
- calendars disabled.
- authentication error.
- incorrect params.
- bad serialization.
(sometimes just die() with message and sometimes performing a redirect)
It would be better to always send one correct iCalendar (RFC 2445) reply instead, so the clients accessing moodle calendars would behave better.
So we must research if the standard provides any facility to return erroneous situations, and use it if possible, replacing those die()/redirect() ends.