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Predicate xrds_specified_location/2
 xrds_specified_location(+URL, -XRDSLocation) is nondet[multifile, library(http/yadis)]
Hook that allows for specifying locations of XRDS documents. For example, Google does not reply to Yadis discovery messages. We can fake it does using:

If this hook succeeds with XRDSLocation bound to - (minus), we assume there is no XRDS document associated to URL. This can be used to avoid retrieving misleading or broken XRDS documents.

 yadis:xrds_specified_location(+Server, -XRDSLocation)[multifile, 'openid.pl']
Hacks to deal with broken Yadis support.
  • Google does not support Yadis discovery, but does have an XRSD document, so we fake its location.
  • stackexchange.com serves an OP Identifier Element instead of an Claimed Identifier Element when doing Yadis discovery on the real OpenID.