protected function execute(ConduitAPIRequest $request)
 {
     $viewer = $request->getUser();
     // Destroy all web sessions.
     $engine = id(new PhabricatorAuthSessionEngine());
     $engine->terminateLoginSessions($viewer);
     // If we were called via OAuth, destroy the OAuth token.
     $oauth_token = $request->getOAuthToken();
     if ($oauth_token) {
         $oauth_token->delete();
     }
     return null;
 }