Получил решение.Если кто-то ищет это.
try {
InputStream is = new FileInputStream("<CERTIFICATE FILE>");
CertificateFactory cf = CertificateFactory.getInstance("X.509");
Certificate cert = cf.generateCertificate(is);
X509Certificate x509Certificate = (X509Certificate) cert;
PublicKey pk = x509Certificate.getPublicKey();
BasicX509Credential publicCredential = new BasicX509Credential();
publicCredential.setPublicKey(pk);
SignatureValidator signatureValidator = new SignatureValidator(publicCredential);
SignableSAMLObject signableSAMLObject = (SignableSAMLObject) <XML OBJECT>;
Signature signature = signableSAMLObject.getSignature();
signatureValidator.validate(signature);
}catch(Exception ex){
// fail this.
}
Объект XML можно получить из сообщения SAML с помощью маршаллера следующим образом:
String encodedMessage = request.getParameter(PARAM_SAML);
String decodedMessage = new String(Base64.decodeBase64(encodedMessage.getBytes()));
DefaultBootstrap.bootstrap();
BasicParserPool ppMgr = new BasicParserPool();
ppMgr.setNamespaceAware(true);
Document responseRoot = ppMgr.parse(new StringReader(decodedMessage));
UnmarshallerFactory unmarshallFactory = Configuration.getUnmarshallerFactory();
Unmarshaller unmarshaller = unmarshallFactory.getUnmarshaller(responseRoot.getDocumentElement());
XMLObject obj = unmarshaller.unmarshall(responseRoot.getDocumentElement());