del_vpn_user.sh

#!/bin/bash
#
# Script to delete a VPN user for both IPsec/L2TP and Cisco IPsec
#
# Copyright (C) 2018-2021 Lin Song <linsongui@gmail.com>
#
# This work is licensed under the Creative Commons Attribution-ShareAlike 3.0
# Unported License: http://creativecommons.org/licenses/by-sa/3.0/
#
# Attribution required: please include my name in any derivative and let me
# know how you have improved it!

export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
SYS_DT=$(date +%F-%T | tr ':' '_')

exiterr()  { echo "Error: $1" >&2; exit 1; }
conf_bk() { /bin/cp -f "$1" "$1.old-$SYS_DT" 2>/dev/null; }

del_vpn_user() {

if [ "$(id -u)" != 0 ]; then
  exiterr "Script must be run as root. Try 'sudo bash $0'"
fi

if ! grep -qs "hwdsl2 VPN script" /etc/sysctl.conf \
  || [ ! -f /etc/ppp/chap-secrets ] || [ ! -f /etc/ipsec.d/passwd ]; then
cat 1>&2 <<'EOF'
Error: Your must first set up the IPsec VPN server before deleting VPN users.
       See: https://github.com/hwdsl2/setup-ipsec-vpn
EOF
  exit 1
fi

VPN_USER=$1

if [ -z "$VPN_USER" ]; then
cat 1>&2 <<EOF
Usage: sudo bash $0 'username_to_delete'
EOF
  exit 1
fi

if printf '%s' "$VPN_USER" | LC_ALL=C grep -q '[^ -~]\+'; then
  exiterr "VPN username must not contain non-ASCII characters."
fi

case "$VPN_USER" in
  *[\\\"\']*)
    exiterr "VPN username must not contain these special characters: \\ \" '"
    ;;
esac

if [ "$(grep -c "^\"$VPN_USER\" " /etc/ppp/chap-secrets)" = "0" ] \
  || [ "$(grep -c "^$VPN_USER:\\\$1\\\$" /etc/ipsec.d/passwd)" = "0" ]; then
cat 1>&2 <<'EOF'
Error: The specified VPN user does not exist in /etc/ppp/chap-secrets
       and/or /etc/ipsec.d/passwd.
EOF
  exit 1
fi

if [ "$(grep -c -v -e '^#' -e '^[[:space:]]*$' /etc/ppp/chap-secrets)" = "1" ] \
  || [ "$(grep -c -v -e '^#' -e '^[[:space:]]*$' /etc/ipsec.d/passwd)" = "1" ]; then
cat 1>&2 <<'EOF'
Error: Could not delete the only VPN user from /etc/ppp/chap-secrets
       and/or /etc/ipsec.d/passwd.
EOF
  exit 1
fi

cat <<EOF

Welcome! Use this script to delete a VPN user account for both
IPsec/L2TP and IPsec/XAuth ("Cisco IPsec") modes.

Please double check before continuing!

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

VPN user to delete:

Username: $VPN_USER

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

EOF

printf "Do you want to continue? [y/N] "
read -r response
case $response in
  [yY][eE][sS]|[yY])
    echo
    echo "Deleting VPN user..."
    echo
    ;;
  *)
    echo "Abort. No changes were made."
    exit 1
    ;;
esac

# Backup config files
conf_bk "/etc/ppp/chap-secrets"
conf_bk "/etc/ipsec.d/passwd"

# Delete VPN user
sed -i "/^\"$VPN_USER\" /d" /etc/ppp/chap-secrets
# shellcheck disable=SC2016
sed -i '/^'"$VPN_USER"':\$1\$/d' /etc/ipsec.d/passwd

# Update file attributes
chmod 600 /etc/ppp/chap-secrets* /etc/ipsec.d/passwd*

cat <<'EOF'
Done!

EOF

}

## Defer until we have the complete script
del_vpn_user "$@"

exit 0