Using Mutual TLS on the Client Side with Ruby

How to use TLS, client authentication, and CA certificates in Ruby

Create a private key and request a certificate for your Ruby client

Before you can teach your client to speak TLS, you will need a certificate issued by a trusted certificate authority (CA). If your organization already runs its own CA and you have a private key and certificate for your Ruby client, along with your CA's root certificate, you can skip to the next step.

If your organization does not yet run its own internal CA, you can read more about creating and running a CA using the open source smallstep software here.

To get up and running quickly, we recommend creating a free hosted smallstep Certificate Manager authority.

To request a certificate from your CA using the step CLI, bootstrap your CA with step ca bootstrap and run the following command (sub the client name for the actual name / DNS name of your Ruby client).

$ step ca certificate "myuser" client.crt client.key

Your certificate and private key will be saved in client.crt and client.key respectively.

Request a copy of your CA root certificate, which will be used to make sure each application can trust certificates presented by other applications.

$ step ca root ca.crt

Your certificate will be saved in ca.crt.

Make a request from Ruby using mutual TLS

Now, we need only to configure our Ruby client to make authenticated requests using our certificate and private key. The CA root certificate will be used to verify that the client can trust the certificate presented by the server.

Pass your certificate, private key, and root CA certificate to Net::HTTP to authenticate your request over TLS.

For additional security, step certificates are signed by an intermediate CA by default rather than the root CA. The intermediate certificate is bundled into your client.crt file. Ruby does not offer any mechanism to automatically load bundled certificates, so we will need to parse the individual certificates out of client.crt ourselves.

Further, Net::HTTP has an outstanding bug that excludes the extra_chain_cert parameter, which needs to be passed to OpenSSL to handle our intermediate CA certificate. We'll patch Net::HTTP to make that attribute available.

require 'openssl'
require 'net/http'

# patch Net::HTTP to support extra_chain_cert
class Net::HTTP
  SSL_IVNAMES << :@extra_chain_cert unless SSL_IVNAMES.include?(:@extra_chain_cert)
  SSL_ATTRIBUTES << :extra_chain_cert unless SSL_ATTRIBUTES.include?(:extra_chain_cert)

  attr_accessor :extra_chain_cert
end

# ...

# parse the client certificate and intermediate CA certificate from client.crt
bundle = File.read('client.crt')
bundle_certs = bundle.scan(/-----BEGIN CERTIFICATE-----(?:.|\n)+?-----END CERTIFICATE-----/)
client_cert = OpenSSL::X509::Certificate.new(bundle_certs[0])
intermediate_cert = OpenSSL::X509::Certificate.new(bundle_certs[1])

options = {
  use_ssl: true,
  verify_mode: OpenSSL::SSL::VERIFY_PEER,
  cert: client_cert,
  extra_chain_cert: [intermediate_cert],
  key: OpenSSL::PKey::EC.new(File.read('client.key')),
  ca_file: 'ca.crt'
}

http = Net::HTTP.start('myserver.internal.net', 443, options)

response = http.request Net::HTTP::Get.new '/'
# do something with response...

# ...

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Automate certificate renewal

By default, step-ca issues certificates with a 24 hour expiration. Short-lived certificates have many benefits but also require that you renew your certificates each day before they expire. How you renew certificates is often dependent on how you deploy your application. See the step-ca certificate lifecycle management docs for more information.

All documentation content from the Hello mTLS project is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).