SecretKey key = new SecretKeySpec(hmacKey, signatureAlgorithm);
properties.setSignatureKey(key);
properties.setSignatureAlgorithm(signatureAlgorithm);
SecurePart securePart = new SecurePart(
new QName("urn:example:po", "PaymentInfo"),
SecurePart.Modifier.Content,
new String[]{"http://www.w3.org/2001/10/xml-exc-c14n#"},
"http://www.w3.org/2000/09/xmldsig#sha1");
properties.addSignaturePart(securePart);