Add SSO cookie authentication support

[pyarmak]

Description

Often times these types of applications will be deployed as a complement to a full stack of applications that use Plex to authenticate users. It would be very useful to be able to have SSO for these scenarios to provide a better user experience. SSO providers include Organize, Authentik, etc.

Desired behavior

A user signs in through an authentication done upstream where a cookie with the Plex token is set, e.g. X-Plex-Token plex-rewind then looks for this cookie and authenticates the user session thereby skipping the login page.

Additional context

I would be happy to test out assist with developing this feature. I am not very familiar with nextjs so if you can point me in the right direction I'll be happy to take a stab at it!

[RaunoT]

Thanks for the ticket and POC PR. Just letting you know that I'm busy on other projects currently, but will pick this up when possible 🙏