Wait a second.
I’m reading this as:
- You’ve developed an application.
- You don’t handle logins into your application yourself, you use Auth0 for that.
- You want Discourse to do SSO against your application, not against Auth0 directly.
If that’s the case, Auth0 doesn’t have anything to do with Discourse specifically. (If you want Discourse to authenticate against Auth0 directly, there are some topics on that, but I personally have no idea how that works.)
None 
The flow is:
- You send the user to Discourse’s
/session/ssoURL, no parameters required. - Discourse sends the user back to you, carrying the nonce.
- You sign the request and send the user to Discourse, submitting your signed ticket.