feat: run optional user startup script (#3)

Signed-off-by: Aurora Gaffney <aurora@blinklabs.io>

Author: agaffney

README.md

@@ -9,3 +9,6 @@ There is no default config provided by the image, so you'll need to provide your
 ```
 docker run -d -n openvpn -v /path/to/openvpn.conf:/etc/openvpn/openvpn.conf ghcr.io/blinklabs-io/openvpn --config /etc/openvpn/openvpn.conf
 ```
+
+The image provides for the ability to provide a custom startup script. It looks for a user script at `/usr/local/bin/entrypoint-user.sh` by default,
+but the location can be overridden with the `USER_STARTUP_SCRIPT` environment variable

bin/entrypoint

@@ -2,6 +2,8 @@
 
 CONFIG_DIR=/etc/openvpn
 
+USER_STARTUP_SCRIPT=${USER_STARTUP_SCRIPT:-/usr/local/bin/entrypoint-user.sh}
+
 ENABLE_NAT=${ENABLE_NAT:-1}
 NAT_SOURCE=${NAT_SOURCE:-10.8.0.0/24}
 NAT_DEVICE=${NAT_DEVICE:-eth0}
@@ -16,4 +18,10 @@ if [[ $ENABLE_NAT = 1 ]]; then
 	iptables -t nat -A POSTROUTING -s ${NAT_SOURCE} -o ${NAT_DEVICE} -j MASQUERADE
 fi
 
+# Execute user startup script if it exists
+if [[ -e ${USER_STARTUP_SCRIPT} ]]; then
+	chmod a+x ${USER_STARTUP_SCRIPT}
+	${USER_STARTUP_SCRIPT}
+fi
+
 exec openvpn --config ${CONFIG_DIR}/openvpn.conf --cd ${CONFIG_DIR} $@