wget -O - https://swupdate.openvpn.net/repos/repo-public.gpg|apt-key add -
echo "deb http://build.openvpn.net/debian/openvpn/stable stretch main" > /etc/apt/sources.list.d/openvpn-aptrepo.list
apt update && apt install openvpn

adduser --system --shell /usr/sbin/nologin --no-create-home ovpn
groupadd ovpn
usermod -g ovpn ovpn

openvpn --genkey --secret /etc/openvpn/server/ta.key
openssl genpkey -genparam -algorithm DH -out /etc/openvpn/server/dhp4096.pem -pkeyopt dh_paramgen_prime_len:4096