Passwordless signin via link generated by api

My problem is not SSO. Discourse is already the source of authentication for my users.
they login to my app, I do an api call to discourse to see if the user/pass is correct
now inside app there are some topics from my forum shown. I want the user to be able to click on that topic and a browser or perhaps webview would open that topic while the user is already logged in to the browser too.