Flarum\Http\Middleware\StartSession::__invoke PHP Method

    public function __invoke(Request $request, Response $response, callable $out = null)
    {
        $session = $this->startSession();
        $request = $request->withAttribute('session', $session);
        $response = $out ? $out($request, $response) : $response;
        $response = $this->withCsrfTokenHeader($response, $session);
        return $this->withSessionCookie($response, $session);
    }