Adding a header to a XML message in Synapse

Using Synapse 2.1, I am trying to transform an XML message with no header into a SOAP message with a header containing credentials to consume a web service. Something like this:

Synapse incoming message:

<SOAP-ENV:Envelope>
<SOAP-ENV:Body>
   ...TAGS...
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

Synapse outgoing message:

<SOAP-ENV:Envelope>
<SOAP-ENV:Header>
   <yta:Authentication>
      <yta:UserName>srnm</yta:UserName>
      <yta:Password>psswrd</yta:Password>
   </yta:Authentication>
</SOAP-ENV:Header>
<SOAP-ENV:Body>
   ...TAGS...
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

How could I configure Synapse to do it? I am successfully using a transform file to update the body of the message, but not to add a header to the output.

I tried using the header and property mediators in the configuration file, but I am not sure what is the way to go. Reading about the header mediator it says "At the moment set header only supports simple valued headers". Could this be the case?

Thanks

Solution

For the record, I ended up using a script mediator with an inline javascript script in the configuration file using the addHeader method. See below:

<script language="js">
   <![CDATA[
     var user = mc.getPayloadXML()..*::UserName.toString();
     var psswd = mc.getPayloadXML()..*::Password.toString();
     mc.addHeader(false, <yta:Authentication xmlns:yta="yta:namespace url"><yta:UserName>{user}</yta:UserName><yta:Password>{psswd}</yta:Password></yta:Authentication>);
   ]]>
</script>