I think the problem is not with the docker image but you’re using an old configuration property that’s no longer used.
See http://extensions.xwiki.org/xwiki/bin/view/Extension/LDAP/Authenticator/#H8.3.x (see also http://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Authentication/#HGenericLDAPconfiguration).
You need to use:
xwiki.authentication.authclass=org.xwiki.contrib.ldap.XWikiLDAPAuthServiceImpl
Thanks