When the SSO Provider option is enabled, user should be logged into Discourse when they click the Start Discussion, or Continue Discussion link at the bottom of a post. If this isn’t working for you, let me know.
If you are not displaying comments on WordPress, or would like users to be logged into Discourse from links other than the comment links, you need to manually create a link in this form:
<a href="https://forum.example.com/session/sso?return_path=https://forum.example.com/your-discourse-endpoint">Link Text</a>
This will cause Discourse to login the user and redirect them to the value set in the
return_path parameter. You can set the return path to
/ to redirect users to your homepage.