code: public function useProxy($proxy, $username, $password)
      {
          if (! $proxy) {
              $this->proxy = false;
  
              return;
          }
          if ((strncmp($proxy, 'http://', 7) != 0) && (strncmp($proxy, 'https://', 8) != 0)) {
              $proxy = 'http://' . $proxy;
          }
          $this->proxy          = new SimpleUrl($proxy);
          $this->proxy_username = $username;
          $this->proxy_password = $password;
      }
docs: Sets proxy to use on all requests for when testing from behind a firewall.
  Set URL to false to disable.
  
  @param string $proxy        Proxy URL.
  @param string $username     Proxy username for authentication.
  @param string $password     Proxy password for authentication.