Perform discovery as you normally do to locate the Yahoo OpenID endpoint. Yahoo returns an XRDS document that includes the Yahoo OpenID endpoint URL. This step corresponds to OpenID OAuth Spec., Section 6.
The Yahoo OpenID Provider verifies a Relying Party's realm and endpoints by making a
Yadis request to the
to discover the realm's OpenID endpoints.
If Yahoo is unable to verify the realm and endpoints, the user will be warned that the user
is signing into an unverified site. Yahoo caches the Yadis document to improve performance
for users who sign into popular sites. For more information, refer to the Yahoo OpenID FAQ.