public function onBefore(BeforeEvent $event)
    {
        $request = $event->getRequest();
        $context = Tracer::spanContext();
        if ($context->enabled()) {
            $request->setHeader($this->propagator->key(), $this->propagator->formatter()->serialize($context));
        }
        $span = Tracer::startSpan([
            'name' => 'GuzzleHttp::request',
            'attributes' => [
                'method' => $request->getMethod(),
                'uri' => $request->getUrl()
            ],
            'kind' => Span::KIND_CLIENT
        ]);
        $this->scope = Tracer::withSpan($span);
    }