It looks like OpenID 2.0 (the only supported by Yahoo) is not supported in ikiwiki. :( I signed up at http://openid.yahoo.com/ , and tried to login to my ikiwiki with the new ID (of the form: https://me.yahoo.com/a-username), but Yahoo told me:
> Sorry! You will not be able to login to this website as it is using an older version of the the OpenID technology. Yahoo! only supports OpenID 2.0 because it is more secure. For more information, check out the OpenID documentation at [Yahoo! Developer Network](http://developer.yahoo.com/openid/).