<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
  <s:Header>
    <Action s:mustUnderstand="1" xmlns="http://schemas.microsoft.com/ws/2005/05/addressing/none">#authenticate</Action>
  </s:Header>
  <s:Body s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <q1:authenticate xmlns:q1="Authenticate">
      <authenticateRequest href="#id1" />
    </q1:authenticate>
    <q2:authenticateRequestType id="id1" xsi:type="q2:authenticateRequestType" xmlns:q2="Authenticate">
      <authenticate href="#id2" />
    </q2:authenticateRequestType>
    <q3:authenticateType id="id2" xsi:type="q3:authenticateType" xmlns:q3="Authenticate">
      <systemKey xsi:type="xsd:string">[systemKey]</systemKey>
      <systemLogin xsi:type="xsd:string">sandbox</systemLogin>
    </q3:authenticateType>
  </s:Body>
</s:Envelope>