Just an example found inside the paypal module
public function makeApiCall($url, $parameters = null, array $headers = null)
{
$server = parse_url($url);
$p = ['url' => $url,
'parameters' => $parameters,
'headers' => $headers
];
if ((substr($server['host'], -10) == 'paypal.com')) {
$p['cafile'] = CLICSHOPPING::BASE_DIR . 'Apps/Payment/PayPal/work/paypal.com.crt';
}
return HTTP::getResponse($p);
}
$p must be inside an array with these elements :
$parameters url, headers, parameters, method, verify_ssl, cafile, certificate, proxy