Previously, once a client was authenticated to the system with an email
link, the user could utilize other email links to other tickets; however,
the same ticket page would be presented to the user regardless of which link
was utilized.

This patch allows the ticket in focus for the user to be changed after
visiting the client portal with a different ticket link.

When following a link from an email, if you are already signed in to the
help desk as a client, you should just be redirected to the new ticket.

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.

Regardless of the configuration of the help desk registration, allow users
to receive ticket links via email. This patch enables the display and
operation of the ticket access link unless a user login is requested by the
user or specifically required by the system.

Instead of always showing the tickets page

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.