If you want users to log in to your Joomla site using their Yahoo credentials, you can do it using our Joomla Yahoo OAuth plugin. Once you configure the Yahoo with the Joomla OAuth plugin, you can allow users to Yahoo SSO into your Joomla site using Yahoo.
Similarly, you can map your Joomla roles based on your Yahoo attributes/groups. To know more about other features we provide in the Joomla OAuth plugin, you can download by click here.