Authenticating Nuxeo users against an LDAP directory is straightforward but for a bug which I encountered.
The instructions for enabling LDAP authentication are here: http://doc.nuxeo.com/display/ADMINDOC/Using+a+LDAP+directory. I am using Tomcat in my case, with OpenDJ as the LDAP server.
The bug I encountered is here: https://jira.nuxeo.com/browse/NXP-6574
And, the workaround I had to implement to get LDAP authentication up and running is detailed here: http://answers.nuxeo.com/questions/701/ad-ldap-connection-issues.
With this in place, LDAP authentication works as expected.