Digest verification fails with SAAJ 1.4+

Hi,

I have an issue with digest verification when using SAAJ versions newer than 1.3. In general my issue is very similar to SANTUARIO-576<https://issues.apache.org/jira/browse/SANTUARIO-576>.

With SAAJ 1.3 everything works as intended, but if I use SAAJ 1.4 (or any newer version, e.g. 3.0.4), the digest verification fails. After some investigation, I noticed that with the new versions there is a type mismatch in org.apache.xml.security.c14n.implementations.CanonicalizerBase which leads to the Signature element not being removed, thus calculating a wrong digest value.
The relevant code is from line 242 onwards:
            case Node.ELEMENT_NODE :
                documentLevel = NODE_NOT_BEFORE_OR_AFTER_DOCUMENT_ELEMENT;
                if (currentNode == excludeNode) {
                    break;
                }

In my case excludeNode is of type com.sun.xml.messaging.saaj.soap.impl.ElementImpl and currentNode is of type com.sun.org.apache.xerces.internal.dom.ElementNSImpl. Therefore, the condition currentNode == excludeNode is not true and the excludeNode is not removed.
The behaviour seems to have changed with SAAJ 1.4 because ElementImpl is no longer extending com.sun.org.apache.xerces.internal.dom.ElementNSImpl. It now has a private element field to store a reference to the actual Element.

A fix for my issue would be replacing
                if (currentNode == excludeNode)
with
               if (excludeNode != null && excludeNode.isSameNode(currentNode))

but maybe there are better fixes. Especially the case from the Jira Ticket, where the class types of currentNode and excludeNode are swapped, would not be fixed with my approach.

Is it possible to fix this in a future version of Santuario? This issue is blocking the JBoss EAP8 migration of our application.

Kind regards,
Lukas Fabian