PHP for saving contact in Constant Contact

function save_contact($first, $last, $email, $phone, $zip) {
  $UN = "<username of your constant contact account, not the developer account>";
  $PW = "<password to the username in $UN>";
  $Key = "<your developer API key, not the secret key>";

  $entry = '<entry xmlns="http://www.w3.org/2005/Atom">
<title type="text"> </title>
<updated>' . date('c') . '</updated>
<author></author>
<id>data:,none</id>
<summary type="text">Contact</summary>
<content type="application/vnd.ctct+xml">
<Contact xmlns="http://ws.constantcontact.com/ns/1.0/"> 
<EmailAddress><![CDATA[' . $email . ']]></EmailAddress>
<FirstName>' . $first . '</FirstName>
<LastName>' . $last . '</LastName>
<PostalCode>' . $zip . '</PostalCode>
<OptInSource>ACTION_BY_CUSTOMER</OptInSource>
<ContactLists>
<ContactList id="https://api.constantcontact.com/ws/customers/' . $UN . '/lists/1" /> 
</ContactLists>
</Contact>
</content>
</entry>';

    // Initialize the cURL session
    $request ="https://api.constantcontact.com/ws/customers/" . $UN . "/contacts";
    $session = curl_init($request);

    // Set up digest authentication
    $userNamePassword = $Key . '%' . $UN . ':' . $PW ;

    // Set cURL options
    curl_setopt($session, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
    curl_setopt($session, CURLOPT_USERPWD, $userNamePassword);
    curl_setopt($session, CURLOPT_POST, 1);
    curl_setopt($session, CURLOPT_POSTFIELDS , $entry);
    curl_setopt($session, CURLOPT_HTTPHEADER, Array("Content-Type:application/atom+xml"));
    curl_setopt($session, CURLOPT_HEADER, false); // Do not return headers
    curl_setopt($session, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($session, CURLOPT_SSL_VERIFYPEER, 0);

    // Execute cURL session and close it
    $response = curl_exec($session);
    curl_close($session);
}