Wildcard DNS

Caddy has an individual cert for every virtual host you create. This is fine, but Let’s Encrypt publishes these as part of certificate transparency and the bad guys are watching. If you create a new site in caddy, you’ll see bots probing for weaknesses within 30 min - without you even having published the URL. There’s no security in anonymity, but the need-to-know principle suggests we shouldn’t be informing the whole world about sites of limited scope.

One solution is a wildcard cert. It’s published as just ‘*.some.org’ so there’s no information disclosed. Caddy supports this, but it requires a little extra work.

Installation

In this example we are already using the default Caddy binary but want to connect to CloudFlare’s DNS service. We must change to a custom Caddy binary for that. Check https://github.com/caddy-dns to see if your DNS provider is available.

# Divert the default binary from the repo
sudo dpkg-divert --divert /usr/bin/caddy.default --rename /usr/bin/caddy
sudo cp /usr/bin/caddy.default /usr/bin/caddy.custom
sudo update-alternatives --install /usr/bin/caddy caddy /usr/bin/caddy.default 10
sudo update-alternatives --install /usr/bin/caddy caddy /usr/bin/caddy.custom 50

# Add the package and restart. 
sudo caddy add-package github.com/caddy-dns/cloudflare
sudo systemctl restart caddy.service    

Because we’ve diverted, apt update will not update caddy. This also stops unattended-updates. You must use caddy upgrade instead. The devs don’t think this should be an issue. I disagree. but you can add a cron job if you like.

DNS Provider Configuration

For Cloudflare, a decent example is below. Just use the ‘Getting the Cloudflare API Token’ part

https://roelofjanelsinga.com/articles/using-caddy-ssl-with-cloudflare/

Caddy Configuration

Use the acme-dns global option and then create a single site (used to determine the cert) and match the actual vhosts with subsites.

{
    acme_dns cloudflare alotcharactersandnumbershere
}

*.some.org, some.org {

    @site1 host site1.some.org
    handle @site1 {
        reverse_proxy * http://localhost:3200
    }

    @site2 host site2.some.org
    handle @site2 {
        root * /srv/www/site2
    }
}