'Accept: application/x-www-form-urlencoded' or 'content-type: application/x-www-form-urlencoded'?

I tried oauthconnector with http://orcid.org/ and can only make it work with 'content-type: application/x-www-form-urlencoded',

--- a/modules/oauth2/lib/DrupalOAuth2Client.inc
+++ b/modules/oauth2/lib/DrupalOAuth2Client.inc
@@ -113,7 +113,7 @@ class DrupalOAuth2Client extends DrupalOAuthClient {
       $url .= '?' . drupal_http_build_query($params);
     }
     $headers = array(
-      'Accept: application/x-www-form-urlencoded',
+      'content-type: application/x-www-form-urlencoded',
       $req->to_header($options['realm']),
     );

'content-type: application/x-www-form-urlencoded' is also used in http://tools.ietf.org/html/rfc6749.