Drupal is not sending external IDs correctly. Instead of the Drupal uid Discourse receives the name.
Per the Discourse SSO specs (https://meta.discourse.org/t/official-single-sign-on-for-discourse-sso/1...) this is something that should never change, thus using name here is incorrect.
external_id is any string unique to the user that will never change, even if their email, name, etc change. The suggested value is your database’s ‘id’ row number.
The fix requires a minor change in includes/discourse_sso.endpoint.inc
'external_id' => $user->name,
to
'external_id' => $user->uid,
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Same here. I successfully tested it on my site; I'll tentatively set the issue status to RTBC.
The 2.0.x branch already sets the Discourse external_id to the Drupal UID, so this issue only affects the 7.x branch.