If the `view.php` page is requested and an auth token is not present in the
URL, do not attempt to sign the user on since it will always fail and will
result in a false "Failed login attempt" warning to the system log.

If a client is already logged into the system and follows a second ticket
link, show the ticket instead of the list of tickets.

SSO was originally used for a SSO plugin. The backend has since been
refactored to support other authentication backends.