Create openvpn config files for openwrt on a PC

openvpn_openwrt.sh

# Change SERVER.DOMAIN.OR.IP in client.ovpn

write_conf(){
    export EASYRSA_CERT_EXPIRE=3650
    export EASYRSA_CRL_DAYS=3650
    export EASYRSA_PKI="pki"
    export EASYRSA_REQ_CN="vpnca"
    cat << 'EOF' > "pki/openssl-easyrsa.cnf"
RANDFILE		= $ENV::EASYRSA_PKI/.rnd

####################################################################
[ ca ]
default_ca	= CA_default		# The default ca section

####################################################################
[ CA_default ]

dir		= $ENV::EASYRSA_PKI	# Where everything is kept
certs		= $dir			# Where the issued certs are kept
crl_dir		= $dir			# Where the issued crl are kept
database	= $dir/index.txt	# database index file.
new_certs_dir	= $dir/certs_by_serial	# default place for new certs.

certificate	= $dir/ca.crt	 	# The CA certificate
serial		= $dir/serial 		# The current serial number
crl		= $dir/crl.pem 		# The current CRL
private_key	= $dir/private/ca.key	# The private key
RANDFILE	= $dir/.rand		# private random number file

x509_extensions	= basic_exts		# The extentions to add to the cert

# This allows a V2 CRL. Ancient browsers don't like it, but anything Easy-RSA
# is designed for will. In return, we get the Issuer attached to CRLs.
crl_extensions	= crl_ext

default_days	= $ENV::EASYRSA_CERT_EXPIRE	# how long to certify for
default_crl_days= $ENV::EASYRSA_CRL_DAYS	# how long before next CRL
default_md	= $ENV::EASYRSA_DIGEST		# use public key default MD
preserve	= no			# keep passed DN ordering

# A few difference way of specifying how similar the request should look
# For type CA, the listed attributes must be the same, and the optional
# and supplied fields are just that :-)
policy		= policy_anything

# For the 'anything' policy, which defines allowed DN fields
[ policy_anything ]
countryName		= optional
stateOrProvinceName	= optional
localityName		= optional
organizationName	= optional
organizationalUnitName	= optional
commonName		= supplied
name			= optional
emailAddress		= optional

####################################################################
# Easy-RSA request handling
# We key off $DN_MODE to determine how to format the DN
[ req ]
default_bits		= $ENV::EASYRSA_KEY_SIZE
default_keyfile 	= privkey.pem
default_md		= $ENV::EASYRSA_DIGEST
distinguished_name	= $ENV::EASYRSA_DN
x509_extensions		= easyrsa_ca	# The extentions to add to the self signed cert

# A placeholder to handle the $EXTRA_EXTS feature:
#%EXTRA_EXTS%	# Do NOT remove or change this line as $EXTRA_EXTS support requires it

####################################################################
# Easy-RSA DN (Subject) handling

# Easy-RSA DN for cn_only support:
[ cn_only ]
commonName		= Common Name (eg: your user, host, or server name)
commonName_max		= 64
commonName_default	= $ENV::EASYRSA_REQ_CN

# Easy-RSA DN for org support:
[ org ]
countryName			= Country Name (2 letter code)
countryName_default		= $ENV::EASYRSA_REQ_COUNTRY
countryName_min			= 2
countryName_max			= 2

stateOrProvinceName		= State or Province Name (full name)
stateOrProvinceName_default	= $ENV::EASYRSA_REQ_PROVINCE

localityName			= Locality Name (eg, city)
localityName_default		= $ENV::EASYRSA_REQ_CITY

0.organizationName		= Organization Name (eg, company)
0.organizationName_default	= $ENV::EASYRSA_REQ_ORG

organizationalUnitName		= Organizational Unit Name (eg, section)
organizationalUnitName_default	= $ENV::EASYRSA_REQ_OU

commonName			= Common Name (eg: your user, host, or server name)
commonName_max			= 64
commonName_default		= $ENV::EASYRSA_REQ_CN

emailAddress			= Email Address
emailAddress_default		= $ENV::EASYRSA_REQ_EMAIL
emailAddress_max		= 64

####################################################################
# Easy-RSA cert extension handling

# This section is effectively unused as the main script sets extensions
# dynamically. This core section is left to support the odd usecase where
# a user calls openssl directly.
[ basic_exts ]
basicConstraints	= CA:FALSE
subjectKeyIdentifier	= hash
authorityKeyIdentifier	= keyid,issuer:always

# The Easy-RSA CA extensions
[ easyrsa_ca ]

# PKIX recommendations:

subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid:always,issuer:always

# This could be marked critical, but it's nice to support reading by any
# broken clients who attempt to do so.
basicConstraints = CA:true

# Limit key usage to CA tasks. If you really want to use the generated pair as
# a self-signed cert, comment this out.
keyUsage = cRLSign, keyCertSign

# nsCertType omitted by default. Let's try to let the deprecated stuff die.
# nsCertType = sslCA

# CRL extensions.
[ crl_ext ]

# Only issuerAltName and authorityKeyIdentifier make any sense in a CRL.

# issuerAltName=issuer:copy
authorityKeyIdentifier=keyid:always,issuer:always
EOF
}

writeserver(){
    cat << EOF > "server.conf"
verb 3
user nobody
group nogroup
dev tun0
port 1194
proto udp
server 192.168.8.0 255.255.255.0
topology subnet
client-to-client
keepalive 10 120
persist-tun
persist-key
duplicate-cn
push "dhcp-option DNS 8.8.8.8"
push "redirect-gateway def1"
push "persist-tun"
push "persist-key"
<dh>
${DH_KEY}
</dh>
<tls-crypt>
${TC_KEY}
</tls-crypt>
<ca>
${CA_CERT}
</ca>
<cert>
${SER_CERT}
</cert>
<key>
${SER_KEY}
</key>
EOF
}

writeclient(){
    cat << EOF > "client.ovpn"
verb 3
dev tun
nobind
client
remote SERVER.DOMAIN.OR.IP 1194 udp
auth-nocache
remote-cert-tls server
<tls-crypt>
${TC_KEY}
</tls-crypt>
<ca>
${CA_CERT}
</ca>
<cert>
${CLI_CERT}
</cert>
<key>
${CLI_KEY}
</key>
EOF
}

wget https://github.com/OpenVPN/easy-rsa/releases/download/v3.0.6/EasyRSA-unix-v3.0.6.tgz
tar xzvf EasyRSA-unix-v3.0.6.tgz
cd EasyRSA-v3.0.6
./easyrsa --batch init-pki
write_conf
./easyrsa --batch gen-dh
./easyrsa --batch build-ca nopass
./easyrsa --batch build-server-full vpnserver nopass
./easyrsa --batch build-client-full vpnclient
openvpn --genkey --secret pki/tc.pem

DH_KEY="$(cat "pki/dh.pem")"
TC_KEY="$(sed -e "/^#/d;/^\w/N;s/\n//" "pki/tc.pem")"
CA_CERT="$(openssl x509 -in "pki/ca.crt")"
SER_CERT="$(openssl x509 -in "pki/issued/vpnserver.crt")"
SER_KEY="$(cat "pki/private/vpnserver.key")"
CLI_CERT="$(openssl x509 -in "pki/issued/vpnclient.crt")"
CLI_KEY="$(cat "pki/private/vpnclient.key")"

writeserver
writeclient

echo Done! You can find config files here:
echo $(pwd)/server.conf
echo $(pwd)/client.ovpn