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