OpenSAML user discussion

I had a similar problem having my service provider validate my signature, and 
it did turn out to be an issue with serialization, as you suggested. 
Specifically, I had indentation turned on in my transformer. Below is the 
code that marshalls and transforms the XML objects into a string value with 
the offending line commented out:

static String xmlObjectToString(XMLObject xmlObject) throws Exception{
        MarshallerFactory marshallerFactory = 
Configuration.getMarshallerFactory();
        Marshaller marshaller = marshallerFactory.getMarshaller(xmlObject);
        Element samlObjectElement = marshaller.marshall(xmlObject);
        Transformer transformer = 
TransformerFactory.newInstance().newTransformer();
        //transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        StreamResult result = new StreamResult(new StringWriter());
        DOMSource source = new DOMSource(samlObjectElement);
        transformer.transform(source, result);
        return result.getWriter().toString();
}