Acme::Client
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
- Acme::Client
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:info@example.com', 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:info@example.com', 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.
Account Key Roll-over
To change the key used for an account you can call #account_key_change
with the new private key or jwk.
require 'openssl'
new_private_key = OpenSSL::PKey::RSA.new(4096)
client.account_key_change(private_key: new_private_key)
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.