Extract a clients SSL certificate

gistfile1.php

<?php

$options = array(
  'ssl'=>array(
		'capture_peer_cert' => true
	)
);

// create our stream context requiring the peers certificate to be returned
$context = stream_context_create($options);

// create our socket connection to the server on the respective port
$socket = stream_socket_client("ssl://[ip_address]:[port]", $errno, $err, 2, STREAM_CLIENT_CONNECT, $context);

// get passed and recieved parameters
$params = stream_context_get_params($socket);

// use OpenSSL to extract the digitial certificate
$cert = openssl_x509_parse($params["options"]["ssl"]["peer_certificate"]);