def extractCredentials(request):
    """ request -> { 'openid.identity' : identity,
                         'openid.assoc_handle' : assoc_handle,
                         'openid.return_to' : return_to,
                         'openid.signed' : signed,
                         'openid.sig' : sig,
                         'openid.invalidate_handle' : invalidate_handle,
                        }
        """
