YvEs2005

Server config :

auth-user-pass-verify /etc/openvpn/ovpnauth.sh via-file

example :  username /password ->  user/user

./ovpnauth.sh md5 user
e2fd12987b9a5a06b1a9383dc3edc6c1

nano ovpnauth.conf

user=e2fd12987b9a5a06b1a9383dc3edc6c1

======================================================

ovpnauth.sh  :

#!/bin/sh

# Config parameters

conf="//etc/openvpn/ovpnauth.conf"
logfile="/var/log/ovpnauth.log"

# End of config parameters

if [ "$1" = "" ] || [ "$1" = "help" ]
then
        echo "ovpnauth.sh v0.1 - OpenVPN sh authentication script with simple user db"
        echo "                   for use withauth-user-pass-verify via-file option"
        echo ""
        echo "help - prints help"
        echo "md5 password - to compute password md5 checksum"
        exit 1
fi

md5(){
        echo "$1.`uname -n`" > /tmp/$$.md5calc
        sum="`md5sum /tmp/$$.md5calc | awk '{print $1}'`"
        rm /tmp/$$.md5calc
        echo "$sum"
}

if [ "$1" = "md5" ]
then
        echo `md5 $2`
        exit 1
fi

log(){
        echo "`date +'%m/%d/%y %H:%M'` - $1" >> $logfile
}

logenv(){
        enviroment="`env | awk '{printf "%s ", $0}'`"
        echo "`date +'%m/%d/%y %H:%M'` - $enviroment" >> $logfile
}

envr="`echo `env``"
userpass=`cat $1`
username=`echo $userpass | awk '{print $1}'`
password=`echo $userpass | awk '{print $2}'`

# computing password md5
password=`md5 $password`
userpass=`cat $conf | grep $username= | awk -F= '{print $2}'`

if [ "$password" = "$userpass" ]
then
        log "OpenVPN authentication successfull: $username"
        logenv
        exit 0
fi

log "OpenVPN authentication failed"
log `cat $1`
logenv
exit 1

reference : 

https://github.com/troydm/ovpnauth.sh