I had to list out users from about 8 OpenVPN servers for detecting any duplicate users which try to connect to 2 or more VPNs by using same username.
My first attempt was using native c to code the program, a web daemon that can read OpenVPN status file and format the output in JSON format to web browser. I almost took a week to completely finish the code. But until now, the program still buggy, sigh. it sometimes crashed after several requests from client. You may find the code here https://github.com/mahadirz/opnvpnstatus .