Nginx users? where?

Hi people! i am new in ROR, i read a lot about it but, i dont found where specific what indeces can see the users of ngingx.

I do this for take the users from nginx, and after? how specific the index for each one
readonlyrest:
access_control_rules:

- name: "Identify a personal kibana index where each user is supposed to save their dashboards"
  kibana_access: rw
  kibana_index: ".kibana_@{x-nginx-user}"

Can please help me?

regards,
Carlos