My problem ended up being that with the Launcher, you can't change the value for java.security.auth.login.config ... so I put my OpenLDAP config in $RDECK_BASE/server/config/jaas-loginmodule.conf. I added a flag to the JVM command line args to pass -Dloginmodule.name=openldap. That flag went into $RDECK_BASE/etc/profile
As for the OpenLDAP configuration ... what you want there will depend on your schema and other details of your LDAP installation.
openldap {
    com.dtolabs.rundeck.jetty.jaas.JettyCachingLdapLoginModule required
    debug="true"
    contextFactory="com.sun.jndi.ldap.LdapCtxFactory"
    bindDn="cn=admin,dc= example,dc=com"
    bindPassword="XXXXXXXX"
    authenticationMethod="simple"
    forceBindingLogin="true"
    userBaseDn="dc=example,dc=com"
    userRdnAttribute="cn"
    userIdAttribute="cn"
    userPasswordAttribute="userPassword"
    userObjectClass="inetOrgPerson"
    roleBaseDn="ou=Groups,dc=example,dc=com"
    roleNameAttribute="cn"
    roleMemberAttribute="uniqueMember"
    roleObjectClass="groupOfUniqueNames"
    cacheDurationMillis="300000"
    reportStatistics="true";
    };
Once that was done, I added 2 new groups to my LDAP server: admin and user.  The people who need access to RunDeck were added to those groups.  I assume that you can change the names of the groups and such ... but I didn't want to dig into things that deeply yet.
Restart RunDeck at this point and give logging in a try.   If you can't login with your LDAP credentials, look in $RDECK_BASE/var/log/service.log.
Hope that you find that helpful,
 - Bruce