luci/applications/luci-app-acme/root/usr/share/rpcd/acl.d/luci-app-acme.json

{
        "luci-app-acme": {
                "description": "Grant UCI access for luci-app-acme",
                "read": {
                        "file": {
                                "/usr/sbin/nginx": [ "read" ],
                                "/usr/sbin/uhttpd": [ "read" ]
                        },
                        "uci": [ "acme" ]
                },
                "write": {
                        "uci": [ "acme" ]
                }
        }
}