DSS sign data
// step 1: generate ToBeSigned data
ToBeSigned dataToSign = service.getDataToSign(toSignDocument, signatureParameters);
// step 2: sign ToBeSigned data using a private key
SignatureValue signatureValue = signingToken.sign(dataToSign, digestAlgorithm, privateKey);
// step 3: sign document using a SignatureValue obtained on the previous step
DSSDocument signedDocument = service.signDocument(toSignDocument, signatureParameters, signatureValue);