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.
Merge pull request #44 from topcoderinc/PEMULA-S-195202

S-195202 - Discourse SSO with tc