I recently created Discourse Phabricator Connector which connect phabricator to Discourse forum.
Its uses OAuth Service provided by phabricator to get the user info.
The current feature is to provide “Login With Phabricator”, that let users login or create account with their phabricator account. With this enabled, in the future, with conduit API, the plugin can be developed to do more advanced stuff like Thread creation, Thread synchronization, Mentions, Admin Synchronization and many stuff.
You can download it here