We fixed this by modifying org.picketlink.identity.federation.core.parsers.util.SAMLParserUtil.parseAuthnContextType(XMLEventReader) by adding one more else if section

          ......
           } else if (JBossSAMLConstants.AUTHN_CONTEXT_CLASS_REF.get().equals(tag)) {
                startElement = StaxParserUtil.getNextStartElement(xmlEventReader);
                String text = StaxParserUtil.getElementText(xmlEventReader);

                AuthnContextClassRefType aAuthnContextClassRefType = new AuthnContextClassRefType(URI.create(text));
                AuthnContextTypeSequence authnContextSequence = authnContextType.new AuthnContextTypeSequence();
                authnContextSequence.setClassRef(aAuthnContextClassRefType);

                authnContextType.setSequence(authnContextSequence);
            } else if (JBossSAMLConstants.AUTHENTICATING_AUTHORITY.get().equals(tag)) {
              // Fix for https://issues.jboss.org/browse/PLINK2-125
              startElement = StaxParserUtil.getNextStartElement(xmlEventReader);
              String text = StaxParserUtil.getElementText(xmlEventReader);
              
              try {
                authnContextType.addAuthenticatingAuthority(new URI(text));
              } catch (URISyntaxException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
              }
            } else
                throw logger.parserUnknownTag(tag, startElement.getLocation());
         ......

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