S-195202 - Discourse SSO with tc

Want to see if we can use the new site login as the generic/redirect
login.

Our forum will be discourse, we want to handle sso based on this

https://meta.discourse.org/t/official-single-sign-on-for-discourse/13045

This is what i am thinking, we will hit the url that will show the login
module, with extra parameters, something like

url=http://talk.topcoder.com/session/sso_login?sso=payload&sig=sig

the site will do the normal auth0 logic as now, but set state to the url
above.

Then our /reg2 callback, after successful login, we will check if there
is sso payload, then we will generate new payload based on the doc, and
redirect back to discourse.