Docs: new documentation site (#2723)

This commit adds a VitePress build to the main repository,
aiming to ditch GitHub Wiki. Moving further, we're going to
host our own documentation site eithor on GitHub Pages or
something alike.

docs/advanced-usages/openconnect.md

@@ -0,0 +1,93 @@
+---
+sidebarTitle: Rule-based OpenConnect
+sidebarOrder: 2
+---
+
+# Rule-based OpenConnect
+
+OpenConnect supports Cisco AnyConnect SSL VPN, Juniper Network Connect, Palo Alto Networks (PAN) GlobalProtect SSL VPN, Pulse Connect Secure SSL VPN, F5 BIG-IP SSL VPN, FortiGate SSL VPN and Array Networks SSL VPN.
+
+For example, there would be a use case where your company uses Cisco AnyConnect for internal network access. Here I'll show you how you can use OpenConnect with policy routing powered by Clash.
+
+First, [install vpn-slice](https://github.com/dlenski/vpn-slice#requirements). This tool overrides default routing table behaviour of OpenConnect. Simply saying, it stops the VPN from overriding your default routes.
+
+Next you would have a script (let's say `tun0.sh`) similar to this:
+
+```sh
+#!/bin/bash
+ANYCONNECT_HOST="vpn.example.com"
+ANYCONNECT_USER="john"
+ANYCONNECT_PASSWORD="foobar"
+ROUTING_TABLE_ID="6667"
+TUN_INTERFACE="tun0"
+
+# Add --no-dtls if the server is in mainland China. UDP in China is choppy.
+echo "$ANYCONNECT_PASSWORD" | \
+  openconnect \
+    --non-inter \
+    --passwd-on-stdin \
+    --protocol=anyconnect \
+    --interface $TUN_INTERFACE \
+    --script "vpn-slice
+if [ \"\$reason\" = 'connect' ]; then
+  ip rule add from \$INTERNAL_IP4_ADDRESS table $ROUTING_TABLE_ID
+  ip route add default dev \$TUNDEV scope link table $ROUTING_TABLE_ID
+elif [ \"\$reason\" = 'disconnect' ]; then
+  ip rule del from \$INTERNAL_IP4_ADDRESS table $ROUTING_TABLE_ID
+  ip route del default dev \$TUNDEV scope link table $ROUTING_TABLE_ID
+fi" \
+    --user $ANYCONNECT_USER \
+    https://$ANYCONNECT_HOST
+```
+
+After that, we configure it as a systemd service. Create `/etc/systemd/system/tun0.service`:
+
+```ini
+[Unit]
+Description=Cisco AnyConnect VPN
+After=network-online.target
+Conflicts=shutdown.target sleep.target
+
+[Service]
+Type=simple
+ExecStart=/path/to/tun0.sh
+KillSignal=SIGINT
+Restart=always
+RestartSec=3
+StartLimitIntervalSec=0
+
+[Install]
+WantedBy=multi-user.target
+```
+
+Then we enable & start the service.
+
+```shell
+chmod +x /path/to/tun0.sh
+systemctl daemon-reload
+systemctl enable tun0
+systemctl start tun0
+```
+
+From here you can look at the logs to see if it's running properly. Simple way is to look at if `tun0` interface has been created.
+
+Similar to the Wireguard one, having an outbound to a TUN device is simple as adding a proxy group:
+
+```yaml
+proxy-groups:
+  - name: Cisco AnyConnect VPN
+    type: select
+    interface-name: tun0
+    proxies:
+      - DIRECT
+```
+
+... and it's ready to use! Add the desired rules:
+
+```yaml
+rules:
+  - DOMAIN-SUFFIX,internal.company.com,Cisco AnyConnect VPN
+```
+
+You should look at the debug level logs when something does not seem right.
+