Merge changes from the 2.6.0 release.
merge from 2.6 branch: add support for EML 2.1.1 to DC crosswalking for OAI provider. https://projects.ecoinformatics.org/ecoinfo/issues/7030
If the client certificate is null, Metacat will throw an exception.
merge from 2.6 branch: use AuthUtils to gather user group subjects
merge to trunk from 2.6 branch: action=validatesession can handle Authorization token
merge to trunk: debugging statements that were added in 2.6 branch
Merge changes from the 2.6.0 branch in MNodeService.allowUpdating() so it honors the localhost MN certificate.
merge from 2.6 branch: use AuthUtils to get group and equivalent identities rather than manually try to extract groups from subject info (can include incorrect groups for given primary subject). https://github.nceas.ucsb.edu/KNB/arctic-data/issues/163
merge from 2.6 branch: use group subject (not name) when translating Session.subjectInfo into group list for Metacat's DocumentImpl. https://github.nceas.ucsb.edu/KNB/arctic-data/issues/163
Add more information on the error message if the client's certificate is not trusted.
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