Passing get variables through https:// ssl secured url

Hey, I'm trying to pass get variables through an https ssl secured url to generate xml data so I can parse it and I'm not sure how to get it working. I have the following code,

I have the url set up like this,

$xml = '
weight_system="IMPERIAL" shipper_number="000222000" destination_postal_code="'.$data5['zip'].'" service_type="1"
';


$xml2 = '
total_pieces="'.$value.'" total_weight="'.$weight.'"
';


$token = 'token';
$base_url = 'https://www.shippingco.com/XML/RatingXML.jsp';


$request_url = $base_url . '?' . http_build_query(array(
'shipment' => '<shipment ' . $xml . '><total ' . $xml2 . '/></shipment>',
'token' => $token
));

and I have an example of the xml data here,

<rating xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="http://www.shippingco.com/XML/rating.xsd">
<rate weight="5.0" weight_unit="lb" zone="3" transit_time="1" transit_time_guaranteed="false" estimated_delivery_date="2013-07-26" base_charge="11.05" freight_charge="11.05"residential_address_charge="2.75" net_charge="13.80" fuel_surcharge_rate="15.8" fuel_surcharge="1.75" subtotal_charge="15.55" on_hst_charge="2.02" total_charge="17.57"/>
</rating>

I have an RSA key, SSL cert, CA bundle and a password and need to use that information to authenticate with the https url. What is the best working way to accomplish this?