This is the simplest answer I could find for a client needing to POST an XML SOAP message to a server in another domain.

Not sure on the security because the POST isn't validated so it just passes on whatever the client sends.

libcurl has a lot of options

$v)
    if(ereg('HTTP_(.+)',$h,$hp))
      echo "
$h = $v
\n";;
*/

# tell the client to expect an xml reply
	header("Content-Type: text/xml");

# then send the the xml reply from the webservice
	echo $xml;

# close the session to free up resources
	curl_close($session);

/* This dumps all the session variables from PHP woo hoo! var_dump(get_defined_vars());  */

?>