#acme #letsencrypt #zerotier


Embeddable ACME server with programmable challenges and storage

3 unstable releases

0.1.1 Feb 17, 2022
0.1.0 Feb 17, 2022
0.0.1 Sep 13, 2021

#5 in #zerotier

43 downloads per month
Used in ca_injector


5.5K SLoC

Coyote: an ACME toolkit

Coyote lets you make ACME servers, which are not guaranteed to not explode in your face. You have to code that out yourself.

coyote aims to solve a few problems (not all of these are solved yet; see "Task List" below):

  • Provide ACME with backing storage you prefer to use, by way of Rust's traits for storage implementation.
  • Provide ACME in non-conforming scenarios (e.g., behind corporate firewalls)
  • Provide ACME services with hooks into the validation system, so you can implement validations however you feel like.
  • It's a library; make it as big or as small as you like. No need for multiple implementations.
  • A FOSS alternative to the letsencrypt canonical implementation that is also tested against LE's test suite.

acmed comes as an example with coyote; it is a complete canonical implementation against PostgreSQL for backing storage. It (deliberately) allows all challenges through and is not meant for production usage.

coyote is intended to let you build an ACME service without using acmed itself, leveraging the traits and tools available in this library for scaffolding. For example, work to implement a Redis based nonce validation system would just be a trait implementation, even though it is not available in this library.

Running acmed

acmed is a very small, example implementation of coyote, intended to demonstrate usage of it. It is not meant or designed to be used in a production environment. It does not perform challenges properly, allowing all of them that come in.

You'll need docker to launch the postgres instance. Plain HTTP works better with certbot for testing so you don't have to dink with your roots; if you want to use caddy or other ACME clients you will need to use a HTTPS enabled service, see "TLS" below.

To launch:

$ make postgres
$ cargo run --example acmed

It will start a service on which you can then pass as the --server flag to certbot, e.g.:

certbot --server '' certonly --standalone -d 'foo.com' -m 'erik+github@hollensbe.org' --agree-tos

Running acmed-tls

We provide the TLS example as acmed-tls; just provide HOSTNAME to set a host name for TLS service; otherwise localhost is assumed. A CA at ca.pem and ca.key will be generated at the directory you run the cargo commands from, which you will need to pass to clients to your certificates. Also, a TLS in-memory cert will be generated to serve the acmed instance. It will start a service on https://${HOSTNAME}:8000 which you can then pass as the acme_ca global directive in caddy.

Otherwise, the use is the same.

Accessing the database

To access the postgres instance that acmed is running against (provided by make postgres):

psql -U postgres -h localhost coyote


docker is required to run the tests. The tests take around 70 seconds to run on a 5900X and use all 24 threads most of the test runtime. Be mindful of the time they take, especially when running them on a slower system.

cargo test

Task List

JOSE/ACME Protocols:

  • JWS decoding; serde codec (handled in middleware)
  • JWK conversion to openssl types; signing and validation
  • Full validation and production of nonce
  • Full validation of ACME protected header (in middleware)
  • RFC7807 "problem details" HTTP error return values
  • Various validating codecs for ACME structs
  • MAYBE: rate limiting (see 6.6 of RFC8555), but probably later
  • Integration of well-used third party ACME client in testing


  • Nonce Handlers
  • Nonce Middleware
  • Accounts (RFC8555 7.3)
    • Handlers:
      • New Account
      • Lookup Account
      • De-registration
  • Orders (RFC8555 7.4)
    • Challenge Traits
      • HTTP basic impl: needed for certbot tests
      • MAYBE: DNS basic impl; see "Other concerns" below
    • Handlers:
      • Authorization Request
      • Fetch challenges
      • Initiate Challenge
      • Deactivate Challenge
      • Challenge status
      • Finalization
      • Fetch Certificate
      • Revocation of Certificate
  • Other concerns:
    • Key Changes (/key-change endpoint, see RFC8555 7.3.5)
    • Find a good solution to DNS challenges (trust-dns-client maybe?)


  • DB Layer
    • PostgreSQL implementation
    • Nonce storage
    • Account storage
    • Order information / state machine storage
    • Cert storage
      • Encrypted at rest

Things coyote doesn't currently handle

These are things that are not covered by our initial goals, and we do not feel they are higher priority items. We will happily accept pull requests for this functionality.

  • Accounts:
    • Terms of Service changes
    • External Account Bindings


This software is covered by the BSD-3-Clause License. See LICENSE.txt for more details.


~839K SLoC