Unable to add "luci admin" as non-root user using luci interface.

I'm stuck at this place where there is no option to define or add user as luci-admin by logging an as non-root (sudo) user in luci interface. So, i replicated a test env in which i logged in as root user and then added luci-admin, so compared this setup with another setup where login as root is restricted, but could not track, where luci-admin user added. This setup is on rhel 6.7 release. I assume there is no easy way out here to get this done..

any help or input regarding this is appreciated.