Thanks for your reports on this issue. We're looking into this now and will hopefully have an update for you here soon.
UPDATE 18:39 - One of our content delivery networks seems to be the source of the problem. We've since disabled the use of this particular CDN and seeing players able to log in again.
Once we've confirmed that this CDN has resolved the issues on their end we will re-enable them, but players should be able to login just fine now.
UPDATE 22:43 - New Zealand players were still experiencing this issue until recently, we made another change a little while ago to rectify and this seems to have solved it for almost every player. We've since confirmed this is a global issue and still working on the primary source of the problem so there may be a few players who experience trouble until the primary CDN is back online.