It wold appear you must use the Login link at the top-right of <a href="https:&#x2F;&#x2F;thimble.mozilla.org&#x2F;" rel="nofollow">https:&#x2F;&#x2F;thimble.mozilla.org&#x2F;</a>.  That sends you to a login page with a bunch of extra parameters after the <a href="https:&#x2F;&#x2F;id.webmaker.org&#x2F;login?" rel="nofollow">https:&#x2F;&#x2F;id.webmaker.org&#x2F;login?</a>.<p>e.g. <a href="https:&#x2F;&#x2F;id.webmaker.org&#x2F;login?client_id=wm_id_wMvw9BSwq2A480dxr&amp;response_type=code&amp;state=e9baaf0a-07e0-497d-85d7-72a7eefc36&amp;scopes=user%20email" rel="nofollow">https:&#x2F;&#x2F;id.webmaker.org&#x2F;login?client_id=wm_id_wMvw9BSwq2A480...</a><p>If you try to login just from <a href="https:&#x2F;&#x2F;id.webmaker.org&#x2F;login" rel="nofollow">https:&#x2F;&#x2F;id.webmaker.org&#x2F;login</a> you will get the error you saw.