alpine-server-setup/services/wireguard/wireguard.policy.json

{
    "description": "Allow Wireguard server access from the internet",
    "service": {
        "wireguard": { "port": 51820, "proto": "udp" }
    },
    "filter": [
        {
            "in": "WAN",
            "out": "_fw",
            "service": "wireguard",
            "action": "accept"
        }
    ]
}