public function perform(OperationInterface $operation, ConfigurationInterface $configuration)
{
$preparedRequestParams = $this->prepareRequestParams($operation, $configuration);
$queryString = $this->buildQueryString($preparedRequestParams, $configuration);
$uri = new Uri(sprintf($this->requestTemplate, $configuration->getCountry(), $queryString));
$request = new \GuzzleHttp\Psr7\Request('GET', $uri->withScheme($this->scheme), ['User-Agent' => 'ApaiIO [' . ApaiIO::VERSION . ']']);
$result = $this->client->send($request);
return $result->getBody()->getContents();
}