public function caFile($sslPath = NULL)
{
$sslPath = $sslPath ? $sslPath : DIRECTORY_SEPARATOR . '..' . DIRECTORY_SEPARATOR . 'ssl' . DIRECTORY_SEPARATOR;
$caPath = __DIR__ . $sslPath . 'api_braintreegateway_com.ca.crt';
if (!file_exists($caPath)) {
throw new Exception\SSLCaFileNotFound();
}
return $caPath;
}