<HMAC name="HMAC-Fail-7">
  <Algorithm>SHA-256</Algorithm>
  <Message>{template_for_message}</Message>
  <!-- missing SecretKey -->
  <!--
      <SecretKey>SECRET123</SecretKey>
  -->
  <Output encoding='base16'>output_value</Output>
  <VerificationValue ref='variable_name'/> <!-- optional -->
</HMAC>
