trillium-acme helps you serve HTTPS with Trillium using automatic certificates, via Let’s Encrypt and ACME tls-alpn-01 challenges.

To use trillium-acme, create an AcmeConfig to configure the certificate you want, then call trillium_acme::new to create an Acceptor and a future. Spawn the future using the same stopper as the server, then pass the Acceptor to the server configuration:

use trillium_acme::AcmeConfig;
use trillium_acme::rustls_acme::caches::DirCache;

let config = AcmeConfig::new(["domain.example"])
    .contact_push("mailto:admin@example.org")
    .cache(DirCache::new("/srv/example/acme-cache-dir"));

let (acceptor, future) = trillium_acme::new(config);
let stopper = trillium_smol::Stopper::new();
let future = stopper.stop_future(future);
trillium_smol::spawn(async {
    future.await;
});
trillium_smol::config()
    .with_port(443)
    .with_host("0.0.0.0")
    .with_nodelay()
    .with_acceptor(acceptor)
    .with_stopper(stopper)
    .run(|conn: trillium::Conn| async move {
       conn.ok("Hello TLS!")
    });

This will configure the TLS stack to obtain a certificate for the domain domain.example, which must be a domain for which your Trillium server handles HTTPS traffic.

On initial startup, your server will register a certificate via Let's Encrypt. Let's Encrypt will verify your server's control of the domain via an ACME tls-alpn-01 challenge, which the TLS listener configured by trillium-acme will respond to.

You must supply a cache via AcmeConfig::cache or one of the other cache methods. This cache will keep the ACME account key and registered certificates between runs, needed to avoid hitting rate limits. You can use rustls_acme::caches::DirCache for a simple filesystem cache, or implement your own caching using the rustls_acme cache traits.

By default, trillium-acme will use the Let's Encrypt staging environment, which is suitable for testing purposes; it produces certificates signed by a staging root so that you can verify your stack is working, but those certificates will not be trusted in browsers or other HTTPS clients. The staging environment has more generous rate limits for use while testing.

When you're ready to deploy to production, you can call .directory_lets_encrypt(true) to switch to the production Let's Encrypt environment, which produces certificates trusted in browsers and other HTTPS clients. The production environment has stricter rate limits.

trillium-acme builds upon the rustls-acme crate.