This actually looks more like a bug in the 18.0.1 XWiki pom where xwiki.enforcer.enforce-jdom2.skip does not seem to inherit xwiki.enforcer.skip by default. You can workaround this by either:
setting <xwiki.enforcer.enforce-jdom2.skip> Maven property to true too
or excluding org.xwiki.platform:xwiki-platform-oldcore from org.xwiki.contrib.ldap:ldap-authenticator dependency
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