Consume SAMLResponse Token

Question

SAML sp-based authentication has following short workflow.

• User wants to access application at sp.
• sp sends SAMLRequest token to idp.
• idp consume it and generate SAMLResponse token.
• idp sends this SAMLResponse token to AC-URL given by sp.

My Question is how sp consume this SAMLResponse token. What is the logic? If I can get some JAVA code help it will be beneficial.

Answer 1

The next recipe is working for me:

1. Get the SAMLResponse token and decode it and inflate:

   // Base64 decode
   Base64 base64Decoder = new Base64();
   byte[] xmlBytes = encodedXmlString.getBytes("UTF-8");
   byte[] base64DecodedByteArray = base64Decoder.decode(xmlBytes);
   
   // Inflate (uncompress) the AuthnRequest data
   // First attempt to unzip the byte array according to DEFLATE (rfc 1951)
   
   Inflater inflater = new Inflater(true);
   inflater.setInput(base64DecodedByteArray);
   // since we are decompressing, it's impossible to know how much space we
   // might need; hopefully this number is suitably big
   byte[] xmlMessageBytes = new byte[5000];
   int resultLength = inflater.inflate(xmlMessageBytes);
   
   if (!inflater.finished()) {
       throw new RuntimeException("didn't allocate enough space to hold "
               + "decompressed data");
   }
   
   inflater.end();
   
   String decodedResponse = new String(xmlMessageBytes, 0, resultLength,
           "UTF-8");
   
   return decodedResponse;
   

2. Parse the resulting XML. Here you can get the info that you need and for example, create a POJO with it (this is a sample code for parsing LogoutRequest's but would be analogous for responses):

   // Parse the XML. SAX approach, we just need the ID attribute
   SAXParserFactory saxParserFactory = SAXParserFactory.newInstance();
   
   // If we want to validate the doc we need to load the DTD
   // saxParserFactory.setValidating(true);
   
   // Get a SAXParser instance
   SAXParser saxParser = saxParserFactory.newSAXParser();
   
   // Parse it
   XMLhandler xmLhandler = new XMLhandler();
   saxParser.parse(new ByteArrayInputStream(xmlLogoutRequest.getBytes()),
           xmLhandler);
   
   // Return the SamlVO
   return xmLhandler.getSamlVO();
   

For my use case I am interesting in only a few elements, so I am using SAX:

public class XMLhandler extends DefaultHandler {

    private SamlVO samlVO;

    public XMLhandler() {
        samlVO = new SamlVO();
    }

    @Override
    public void startElement(String uri, String localName, String qName,
        Attributes attributes) throws SAXException {

        // Managing a LogoutRequest means that we are going to build a LogoutResponse
        if (qName.equals("samlp:LogoutRequest")) {
            // The ID value of a request will be the LogoutResponse's InReponseTo attribute 
            samlVO.setInResponseTo(attributes.getValue("ID"));
            // From the destination we can get the Issuer element
            String destination = attributes.getValue("Destination");
            if (destination != null) {
                URL destinationUrl = null;
                try {
                    destinationUrl = new URL(destination);
                } catch (MalformedURLException e) {
                     // TODO: We could set the server hostname (take it from a property), but this URL SHOULD be well formed!
                     e.printStackTrace();
                }
                samlVO.setIssuer(destinationUrl.getHost());
            }
        }   
    }

    public SamlVO getSamlVO() {
        return samlVO;
    }

}

Hope it helps,

Luis

PS: you also can use a library like OpenSAML

DefaultBootstrap.bootstrap();

HTTPRedirectDeflateDecoder decode = new HTTPRedirectDeflateDecoder(new BasicParserPool());
BasicSAMLMessageContext<LogoutRequest, ?, ?> messageContext = new BasicSAMLMessageContext<LogoutRequest, SAMLObject, SAMLObject>();
messageContext.setInboundMessageTransport(new HttpServletRequestAdapter(request));
decode.decode(messageContext);
XMLObjectBuilderFactory builderFactory = org.opensaml.Configuration.getBuilderFactory();
LogoutRequestBuilder logoutRequestBuilder = (LogoutRequestBuilder) builderFactory.getBuilder(LogoutRequest.DEFAULT_ELEMENT_NAME);
LogoutRequest logoutRequest = logoutRequestBuilder.buildObject();
logoutRequest = (LogoutRequest) messageContext.getInboundMessage();

But be prepared to include a few libraries in your CLASSPATH!!!