Content authentication sets up the Tiki to be able to connect to remote sites with authentication, thus being able to receive data and information from that site either with authentication or otherwise in a way that is more complicated than just a direct download.
Content authentication is configured on the same setting configuration page as Admin DSN, and can be accessed on the Admin Panel (i.e. Control Panels page) under the Tools dropdown, or at tiki-admin_dsn.php.
This is used by a number of features, and will need to be configured, such as: