Added in Tiki21: CardDAV support in Tiki via SabreDAV to sync Contacts.
CardDAV URL is http://example.org/tiki-carddav.php but you should point to the base URL and let your CardDAV client auto-detect settings.
Tested with https://f-droid.org/en/packages/at.bitfire.davdroid/
Beyond Contacts, it can also sync users which have accounts in your Tiki instance.