It defaults to the `cgiurl` (or `openid_cgiurl` if set); only allowing
ikiwiki's [[CGI]] to authenticate. If you have multiple ikiwiki instances,
or other things using openid on the same site, you may choose to put them
- all in the same realm to improve the user's openid experience.
+ all in the same realm to improve the user's openid experience. It is an
+ url pattern, so can be set to eg "http://*.example.com/"
* `openid_cgiurl` can be used to cause a different than usual `cgiurl`
to be used when doing openid authentication. The `openid_cgiurl` must