The recent OAuth security fix [1] had a bug [2] which caused some legitimate OAuth requests to be rejected. The affected versions have been updated to work properly. Apologies for the disruption.
Gergő https://www.mediawiki.org/wiki/User:Tgr_(WMF)
[1] https://lists.wikimedia.org/pipermail/mediawiki-announce/2016-October/000197... [2] https://phabricator.wikimedia.org/T149194
mediawiki-announce@lists.wikimedia.org