[flexcoders] mx:request equivalent in actionscript??

[luvfotography]

Hi, how do I code the 'mx:request' in actionscript?
example:

   <mx:HTTPService id="form1" url="{phpFile}" method="GET" resultFormat="text" 
result="{textarea1.text = String(event.result)}">
     <mx:request>
        <username>{username.text}</username>
     </mx:request>
   </mx:HTTPService>

I don't see any methods on the Httpservice class to add any 'request' 
parameters.