Handle when IDP does not use namespace prefix on CanonicalizationMethod

[james-async]

The "Novell Access Manager" does not put a namespace prefix on the CanonicalizationMethod element. (or at least the installed version we are working with does not). We tried to write a test. This is a minimalist change rather than changing childPath.

In fact the official documentation shows that the namespace prefix is not applied to CanonicalizationMethod.
https://www.netiq.com/documentation/access-manager-43/admin/data/b65ogn0.html
<ds:SignedInfo> <CanonicalizationMethod xmlns="http://www.w3.org/2000/09/xmldsig#" Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/> <ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/> <ds:Reference URI="#idF5JceWGWYwS3bOkmJS2wJuNqitU"> <ds:Transforms> <ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/> <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/> </ds:Transforms> <ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/> <DigestValue xmlns="http://www.w3.org/2000/09/xmldsig#">ZocFiEUYcda0cKGRNcZYZqvmnlM=</DigestValue> </ds:Reference> </ds:SignedInfo>

[russellhaering]

Good find, you uncovered some old code that has an actual bug in it. That CanonicalizationMethod has a namespace declared and we should have been respecting it.

Can you test this branch and confirm that it fixes the issue for you?

https://github.com/russellhaering/goxmldsig/tree/russell_h/improved_namespace_handling_2