Oauth user Authorisation

I work with Oauth 1. I want when the user enters the admin page of my plugin, it is redirected to the site should perform authorization and come back on my page but it does not work get_user_authorization(); do not work.

  session_unset();

  $OAUTH->set_site("http://www.site.com/fr/", $key, $secret);
  $OAUTH->set_callback($callback_url);

  $OAUTH->get_request_token()
      ->get_user_authorization();