[Feature Request] "Default" SSO provider

[baconwaifu]

Is your feature request related to a problem? Please describe.
For instances that only have one provider, requiring the link to be https://jelly.example.com/sso/PROTO/p/[provider name] can get annoying to share, unless you already have it in your clipboard.

Describe the solution you'd like
I Suggest adding a config field for a "default" provider, which would just control a route to /sso or /sso/default (is there even anything at the base /sso route currently?)

Unless/until jellyfin adds a "login mechanisms" API to add buttons to the login screen, this is an easy QoL change for SSO signon

Describe alternatives you've considered

Add a "pick-a-provider" menu to the base route? would require a bit more work than a dumb redirect route though.

Another interesting solution would be to use IAuthenticationProvider like LDAP does, to intercept web login requests for SSO-only users and redirect to the appropriate provider automatically; I think I may look into that later...

[9p4]

Unless/until jellyfin adds a "login mechanisms" API to add buttons to the login screen, this is an easy QoL change for SSO signon

This is already possible! Take a look at https://github.com/9p4/jellyfin-plugin-sso#creating-a-login-button-on-the-main-page