Going to https://idm.wikimedia.org/ which redirects to https://idm.wikimedia.org/wikimedia/login/?next=/ and clicking the Log In button , it shows a very vague
Bitu Error There was an error processing your request. Should the problem persist, you can submit a bug report Click here to return to the frontpage.
I'd expect a better error message to tell me that I need to enable cookies in my web browser.