How to POST XML data in codeigniter?

[eluser]wahyusumartha[/eluser]
i want to develop web service client with codeigniter.. so i have to post data with xml format...

for example :
i want to post this xml :
<customer>
<firstname>wahyu</firstname>
<lastname>sumartha</lastname>
</customer>

xml data above would be post to url (http://example.com:9090/resource/customer/add)

could u help me how to do it ???