public function requestFormDigest()
    {
        $request = new RequestOptions($this->getServiceRootUrl() . "contextinfo");
        $request->Method = HttpMethod::Post;
        $response = $this->executeQueryDirect($request);
        if(!isset($this->contextWebInformation))
            $this->contextWebInformation = new ContextWebInformation();
        $result = new ClientResult($this->contextWebInformation);
        if ($this->getSerializerContext()->MetadataLevel == ODataMetadataLevel::Verbose) {
            $this->getSerializerContext()->RootElement = "GetContextWebInformation";
        }
        $payload = json_decode($response);
        $result->fromJson($payload,$this->getSerializerContext());
    }