@pfaffman the way i did it, the user logs in to thinkific only (there is no discourse sign up/sign up process) You eliminate that by setting the SSO setting to a middleman server.
So it looks like User Clicks Login (on discourse) → Your server to start sso process → redirect to thinkific page to login.
There is a lot more work that goes into doing it this way, but it’s the only solution i could figure that would allow SSO from thinkific (where thinkific is the source of truth).
I started a blog post on this, and will try and finish it today, maybe it will be helpful for you.