We need a discovery service to retrieve the logout URL for a specific openid provider so we can offer it to the client after he log out from our application/website . Basically a short message like "If you want to also logout from Google click here ". Currently only few individual OpenID providers offer different URLs for logout to which the user can be redirected. But there is no discovery service and you have to hard-code these links .
Google: https://www.google.com/accounts/Logout
Yahoo: https://login.yahoo.com/config/login?logout=1