OCA\Richdocuments\Controller\DocumentController::loginUser PHP Method

    private function loginUser($userid)
    {
        $users = \OC::$server->getUserManager()->search($userid, 1, 0);
        if (count($users) > 0) {
            $user = array_shift($users);
            if (strcasecmp($user->getUID(), $userid) === 0) {
                // clear the existing sessions, if any
                \OC::$server->getSession()->close();
                // initialize a dummy memory session
                $session = new \OC\Session\Memory('');
                // wrap it
                $cryptoWrapper = \OC::$server->getSessionCryptoWrapper();
                $session = $cryptoWrapper->wrapSession($session);
                // set our session
                \OC::$server->setSession($session);
                \OC::$server->getUserSession()->setUser($user);
            }
        }
    }