/etc/systemd/system/caddy.service

caddy.service

 [Unit]
Description=Caddy HTTP/2 web server
Documentation=https://caddyserver.com/docs
After=network-online.target
Wants=network-online.target systemd-networkd-wait-online.service

[Service]
Restart=on-failure

User=www-data
Group=www-data

Environment=HOME=/etc/ssl/caddy

ExecStart=/usr/local/bin/caddy -log stdout -agree=true -conf=/etc/caddy/Caddyfile -root=/var/tmp
ExecReload=/bin/kill -USR1 $MAINPID

LimitNOFILE=4096
LimitNPROC=64

PrivateTmp=true
PrivateDevices=true
ProtectHome=true
ProtectSystem=full
ReadWriteDirectories=/etc/ssl/caddy

CapabilityBoundingSet=CAP_NET_BIND_SERVICE
AmbientCapabilities=CAP_NET_BIND_SERVICE
NoNewPrivileges=true

[Install]
WantedBy=multi-user.target