<ds:SignatureMethod xmlns:ds="http://www.w3.org/2000/09/xmldsig#" Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256">
  <ds:HMACOutputLength>1234</ds:HMACOutputLength>
  <ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">Some</ssp:Chunk>
</ds:SignatureMethod>