Hey @shahidmir 
Just wanted to jump in with a quick comment: your best bet is to set up a RWA in Auth0 and use the official Discourse OAuth 2 Basic Plugin.
We, at Auth0, have a similar setup where our customers can login to the Auth0 Dashboard, Support Center, and Community with a single Auth0 account. If the user has already created a session with your app, your Auth0 tenant will automatically return them to Discourse with the access_token without prompting them for their credentials.
You can take a look at how we set it up at community.auth0.com
I hope that helps 