Crate acme_lib

source ·
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acme-lib is a library for accessing ACME (Automatic Certificate Management Environment) services such as Let’s Encrypt.

Uses ACME v2 to issue/renew certificates.


use acme_lib::{Error, Directory, DirectoryUrl};
use acme_lib::persist::FilePersist;
use acme_lib::create_p384_key;

fn request_cert() -> Result<(), Error> {

// Use DirectoryUrl::LetsEncryptStaging for dev/testing.
let url = DirectoryUrl::LetsEncrypt;

// Save/load keys and certificates to current dir.
let persist = FilePersist::new(".");

// Create a directory entrypoint.
let dir = Directory::from_url(persist, url)?;

// Reads the private account key from persistence, or
// creates a new one before accessing the API to establish
// that it's there.
let acc = dir.account("")?;

// Order a new TLS certificate for a domain.
let mut ord_new = acc.new_order("", &[])?;

// If the ownership of the domain(s) have already been
// authorized in a previous order, you might be able to
// skip validation. The ACME API provider decides.
let ord_csr = loop {
    // are we done?
    if let Some(ord_csr) = ord_new.confirm_validations() {
        break ord_csr;

    // Get the possible authorizations (for a single domain
    // this will only be one element).
    let auths = ord_new.authorizations()?;

    // For HTTP, the challenge is a text file that needs to
    // be placed in your web server's root:
    // /var/www/.well-known/acme-challenge/<token>
    // The important thing is that it's accessible over the
    // web for the domain(s) you are trying to get a
    // certificate for:
    let chall = auths[0].http_challenge();

    // The token is the filename.
    let token = chall.http_token();
    let path = format!(".well-known/acme-challenge/{}", token);

    // The proof is the contents of the file
    let proof = chall.http_proof();

    // Here you must do "something" to place
    // the file/contents in the correct place.
    // update_my_web_server(&path, &proof);

    // After the file is accessible from the web,
    // this tells the ACME API to start checking the
    // existence of the proof.
    // The order at ACME will change status to either
    // confirm ownership of the domain, or fail due to the
    // not finding the proof. To see the change, we poll
    // the API with 5000 milliseconds wait between.

    // Update the state against the ACME API.

// Ownership is proven. Create a private key for
// the certificate. These are provided for convenience, you
// can provide your own keypair instead if you want.
let pkey_pri = create_p384_key();

// Submit the CSR. This causes the ACME provider to enter a
// state of "processing" that must be polled until the
// certificate is either issued or rejected. Again we poll
// for the status change.
let ord_cert =
    ord_csr.finalize_pkey(pkey_pri, 5000)?;

// Now download the certificate. Also stores the cert in
// the persistence.
let cert = ord_cert.download_and_save_cert()?;


§Domain ownership

Most website TLS certificates tries to prove ownership/control over the domain they are issued for. For ACME, this means proving you control either a web server answering HTTP requests to the domain, or the DNS server answering name lookups against the domain.

To use this library, there are points in the flow where you would need to modify either the web server or DNS server before progressing to get the certificate.

See http_challenge and dns_challenge.

§Multiple domains

When creating a new order, it’s possible to provide multiple alt-names that will also be part of the certificate. The ACME API requires you to prove ownership of each such domain. See authorizations.

§Rate limits

The ACME API provider Let’s Encrypt uses rate limits to ensure the API i not being abused. It might be tempting to put the delay_millis really low in some of this libraries’ polling calls, but balance this against the real risk of having access cut off.

§Use staging for dev!

Especially take care to use the Let`s Encrypt staging environment for development where the rate limits are more relaxed.

See DirectoryUrl::LetsEncryptStaging.

§Implementation details

The library tries to pull in as few dependencies as possible. (For now) that means using synchronous I/O and blocking cals. This doesn’t rule out a futures based version later.

It is written by following the ACME draft spec 18, and relies heavily on the openssl crate to make JWK/JWT and sign requests to the API.


  • Low level API JSON objects.
  • Order life cycle.
  • Pluggable persistence.


  • Account with an ACME provider.
  • Encapsulated certificate and private key.
  • Entry point for accessing an ACME API.



  • Make a P-256 private key (from which we can derive a public key).
  • Make a P-384 private key pair (from which we can derive a public key).
  • Make an RSA private key (from which we can derive a public key).

Type Aliases§