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Acme::Client

Build Status

acme-client is a client implementation of the ACMEv2 / RFC 8555 protocol in Ruby.

You can find the ACME reference implementations of the server in Go and the client in Python.

ACME is part of the Letsencrypt project, which goal is to provide free SSL/TLS certificates with automation of the acquiring and renewal process.

You can find ACMEv1 compatible client in the acme-v1 branch.

Installation

Via RubyGems:

$ gem install acme-client

Or add it to a Gemfile:

gem 'acme-client'

Usage

Setting up a client

The client is initialized with a private key and the directory of your ACME provider.

LetsEncrypt's directory is https://acme-v02.api.letsencrypt.org/directory.

They also have a staging endpoint at https://acme-staging-v02.api.letsencrypt.org/directory.

acme-ruby expects OpenSSL::PKey::RSA or OpenSSL::PKey::EC

You can generate one in Ruby using OpenSSL.

require 'openssl'
private_key = OpenSSL::PKey::RSA.new(4096)

Or load one from a PEM file

require 'openssl'
OpenSSL::PKey::RSA.new(File.read('/path/to/private_key.pem'))

See RSA and EC for documentation.

client = Acme::Client.new(private_key: private_key, directory: 'https://acme-staging-v02.api.letsencrypt.org/directory')

If your account is already registered, you can save some API calls by passing your key ID directly. This will avoid an unnecessary API call to retrieve it from your private key.

client = Acme::Client.new(private_key: private_key, directory: 'https://acme-staging-v02.api.letsencrypt.org/directory', kid: 'https://example.com/acme/acct/1')

Account management

Accounts are tied to a private key. Before being allowed to create orders, the account must be registered and the ToS accepted using the private key. The account will be assigned a key ID.

client = Acme::Client.new(private_key: private_key, directory: 'https://acme-staging-v02.api.letsencrypt.org/directory')
account = client.new_account(contact: 'mailto:[email protected]', terms_of_service_agreed: true)

After the registration you can retrieve the account key indentifier (kid).

client = Acme::Client.new(private_key: private_key, directory: 'https://acme-staging-v02.api.letsencrypt.org/directory')
account = client.new_account(contact: 'mailto:[email protected]', terms_of_service_agreed: true)
account.kid # => <kid string>

If you already have an existing account (for example one created in ACME v1) please note that unless the kid is provided at initialization, the client will lazy load the kid by doing a POST to newAccount whenever the kid is required. Therefore, you can easily get your kid for an existing account and (if needed) store it for reuse:

client = Acme::Client.new(private_key: private_key, directory: 'https://acme-staging-v02.api.letsencrypt.org/directory')

# kid is not set, therefore a call to newAccount is made to lazy-initialize the kid
client.kid
=> "https://acme-staging-v02.api.letsencrypt.org/acme/acct/000000"

Obtaining a certificate

Ordering a certificate

To order a new certificate, the client must provide a list of identifiers.

The returned order will contain a list of Authorization that need to be completed in other to finalize the order, generally one per identifier.

Each authorization contains multiple challenges, typically a dns-01 and a http-01 challenge. The applicant is only required to complete one of the challenges.

You can access the challenge you wish to complete using the #dns or #http method.

order = client.new_order(identifiers: ['example.com'])
authorization = order.authorizations.first
challenge = authorization.http

Preparing for HTTP challenge

To complete the HTTP challenge, you must return a file using HTTP.

The path follows the following format:

.well-known/acme-challenge/#{token}

And the file content is the key authorization. The HTTP01 object has utility methods to generate them.

> http_challenge.content_type # => 'text/plain'
> http_challenge.file_content # => example_token.TO1xJ0UDgfQ8WY5zT3txynup87UU3PhcDEIcuPyw4QU
> http_challenge.filename # => '.well-known/acme-challenge/example_token'
> http_challenge.token # => 'example_token'

For test purposes you can just save the challenge file and use Ruby to serve it:

ruby -run -e httpd public -p 8080 --bind-address 0.0.0.0

Preparing for DNS challenge

To complete the DNS challenge, you must set a DNS record to prove that you control the domain.

The DNS01 object has utility methods to generate them.

dns_challenge.record_name # => '_acme-challenge'
dns_challenge.record_type # => 'TXT'
dns_challenge.record_content # => 'HRV3PS5sRDyV-ous4HJk4z24s5JjmUTjcCaUjFt28-8'

Requesting a challenge verification

Once you are ready to complete the challenge, you can request the server perform the verification.

challenge.request_validation

The validation is performed asynchronously and can take some time to be performed by the server.

You can poll until its status changes.

while challenge.status == 'pending'
  sleep(2)
  challenge.reload
end
challenge.status # => 'valid'

Downloading a certificate

Once all required authorizations have been validated through challenges, the order can be finalized using a CSR (Certificate Signing Request).

A CSR can be slightly tricky to generate using OpenSSL from Ruby standard library. acme-client provide a utility class CertificateRequest to help with that. You'll need to use a different private key for the certificate request than the one you use for your Acme::Client account.

Certificate generation happens asynchronously. You may need to poll.

csr = Acme::Client::CertificateRequest.new(private_key: a_different_private_key, subject: { common_name: 'example.com' })
order.finalize(csr: csr)
while order.status == 'processing'
  sleep(1)
  order.reload
end
order.certificate # => PEM-formatted certificate

Ordering an alternative certificate

Let's Encrypt is transitioning to use a new intermediate certificate. Starting January 11, 2021 new certificates will be signed by their own intermediate. To ease the transition on clients Let's Encrypt will continue signing an alternative version of the certificate using the old, cross-signed intermediate until September 29, 2021. In order to utilize an alternative certificate the Order#certificate method accepts a force_chain keyword argument, which takes the issuer name of the intermediate certificate. For example, to download the cross-signed certificate after January 11, 2021, call Order#certificate as follows:

begin
  order.certificate(force_chain: 'DST Root CA X3')
rescue Acme::Client::Error::ForcedChainNotFound
  order.certificate
end

Note: if the specified forced chain doesn't match an existing alternative certificate the method will raise an Acme::Client::Error::ForcedChainNotFound error.

Learn more about the original Github issue for this client here, information from Let's Encrypt here, and cross-signing here.

Extra

Certificate revokation

To revoke a certificate you can call #revoke with the certificate.

client.revoke(certificate: certificate)

Certificate renewal

There is no renewal process, just create a new order.

Not implemented

  • Account Key Roll-over.

Requirements

Ruby >= 2.1

Development

All the tests use VCR to mock the interaction with the server. If you need to record new interaction you can specify the directory URL with the ACME_DIRECTORY_URL environment variable.

ACME_DIRECTORY_URL=https://acme-staging-v02.api.letsencrypt.org/directory rspec

Pull request?

Yes.

License

MIT License