Pseudo code for detecting php version, operating system and a default location for CA bundle.

DefaultCABundle.php

<?
$os = php_uname("s");
$phpversion = floatval(substr(phpversion (),0,3));
if($phpversion<5.6)
{
	if($os=="OS400")
	{
		$defaultcafile = "/QOpenSys/QIBM/ProdData/SC1/OpenSSL/openssl-0.9.7d/cert.pem";
	}
	else if ($os=="Linux")
	{
		$defaultcafile = "/etc/pki/tls/certs/ca-bundle.crt";
	}
}

if(!file_exists($defaultcafile) && $userDidntProvideCABundle)
{
	//possible security issue as you have to trust that the DNS and server below is not compromised.
	$certFromWeb = readfile("http://curl.haxx.se/ca/cacert.pem");
	//::TODO:: cache this cert so we don't send multiple requests. Have to add logic above to see if we have the cached cert 
	$defaultcafile = $certFromWeb;
}