Hi someusers are reporting when registering for an account using MediaWiki OAuth.
They have said the following.
I just tried to report it on Phabricator. From the home page, I clicked "Report a problem", and it took me to a login screen. I clicked the "Mediawiki" button, and it took me to the MediaWiki's OAuth screen. After I clicked "Allow", it came back to Phabricator, and the message, "Login Failure. Login cookie was set correctly, but your login session is not valid. Try clearing cookies and logging in again."