Request URL need to be changed with symphony httpClient()

Problem/Motivation

$ch = curl_init($bitly_api);
      curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
      curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);
      curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
      curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
      $result = curl_exec($ch);
      $resultToJson = json_decode($result);