How to disable connection by one login and password to Openvpn?

Question

linux

There is an Openvpn server on vps Centos 8

server config

duplicate-cn
auth-user-pass-verify /etc/openvpn/verify.sh via-file
username-as-common-name
script-security 2
client-cert-not-required
tmp-dir /etc/openvpn/tmp

client config

client
resolv-retry infinite
nobind
persist-key
persist-tun
remote-cert-tls server
ignore-unknown-option block-outside-dns
block-outside-dns
auth-user-pass
explicit-exit-notify

On the Internet I found such a script for connecting by login and password

#!/bin/sh
## format: username:password username:password ...
## you can even have same usernames with different passwords
# USERS='user1:pass1 user2:pass2 user3:pass3'
## you could put username:password in
## a separate file and read it like this
USERS=`cat /etc/openvpn/user.pass`
vpn_verify() {
if [ ! $1 ] || [ ! $2 ]; then
#echo "No username or password: $*"
exit 1
fi
## it can also be done with grep or sed
for i in $USERS; do
if [ "$i" = "$1:$2" ]; then
## you can add here logging of users
## if you have enough space for log file
#echo `date` $1:$2 >> your_log_file
exit 0
fi
done
}
if [ ! $1 ] || [ ! -e $1 ]; then
#echo "No file"
exit 1
fi
## $1 is file name which contains
## passed username and password
vpn_verify `cat $1`
#echo "No user with this password found"
exit 1

Everything works, it connects, but you can somehow implement a connection using one certificate so that it is impossible to connect with one login and password to several clients at the same time.
Thank you.

Answer 1

https://4admin.info/setup-openvpn-deny-concurrent-...
And take a look at the comments below.

Answer 2

If external authorization is used, and it is used, judging by the attached script, you just need to remove it duplicate-cnfrom the server config.