Can you give a little more detail in what was wrong on the other end so people looking for this error might use this to fix their issues?
I’m one of those, authorizing discourse against mattermost and I’m a little stuck with a similar error:
Started GET "/auth/oauth2_basic/callback?code=<redacted>&state=<redacted>" for <IPv4> at 2020-02-07 13:07:46 +0000
(oauth2_basic) Setup endpoint detected, running now.
(oauth2_basic) Callback phase initiated.
(oauth2_basic) Authentication failure! invalid_credentials: OAuth2::Error,
Started GET "/auth/failure?message=invalid_credentials&origin=https%3A%2F%2F<discourse_FQDN>%2Flogin&strategy=oauth2_basic" for <IPv4> at 2020-02-07 13:07:47 +0000
Processing by Users::OmniauthCallbacksController#failure as HTML
Parameters: {"message"=>"invalid_credentials", "origin"=>"https://<discourse_FQDN>/login", "strategy"=>"oauth2_basic"}
Thanks,
Beam