Tobias Oetterer writes:
There is a new permission available that governs the right to create accounts when logging in with an external user account. It's called "autocreateaccount" [0]. You have to add to your config something like: $wgGroupPermissions['*']['autocreateaccount'] = true;
Or maybe this is enough: $wgGroupPermissions['user']['autocreateaccount'] = true;
We encountered the same problem in the previous release, Mediawiki 1.27, and Tobias's suggested change worked for us.
DanB