Federate PKI trust models between multiple autonomous certificate authorities
foo.internal is running in AWS, and
bar.internal is running in GCP.
To communicate, requests must be sent across the public internet. Traditionally
this sort of cross-connectivity is secured using a network-level tunnel, like
an SSH tunnel or a VPN. These tunnels are often configured and managed ad-hoc.
They can also be challenging to scale and operate and introduce a single point of failure into an otherwise resilient system. With a PKI trust model and automated certificate management, you can leverage mTLS for secure cross-connectivity without a VPN to avoid these issues.
In this scenario, you may want to run two CAs: one in AWS and one in GCP. That
way, you don’t need to expose open source
step-ca to the public internet. To make this
work, these CAs must federate a PKI trust model, which means
bar.internal must trust both CAs to issue certificates.
step ca federation subcommand can be used to distribute the bundle of
federated roots to workloads in both clouds.
About this tutorial
- Learn how to secure comms across clouds using autonomous internal PKI.
- Examples include copy/paste code blocks and clonable code repos.
- When complete, you will have secure cross-connectivity without a VPN.
- Estimated effort: Reading time ~3 mins, Lab time ~10 to 60 mins.
- Open Source - This tutorial assumes you have initialized and started up a
step-cainstance using the steps in Getting Started.
- Smallstep Certificate Manager - Please get in touch with Smallstep Customer Success if you want to federate an existing Root with a Certificate Manager Authority.
The basic federation tutorial below showcases how to securely facilitate communication between relying parties of multiple autonomous certificate authorities.
This tutorial uses a pre-generated PKI. Do not use these pre-generated PKIs for any purposes outside of this tutorial.
You can find all of the code in this tutorial here:
This is what we will cover in this tutorial:
- Launching the federated online CAs
- Bringing up a demo server
- Running the demo client
- Curl as a client
Launching the federated online CAs
If you want to follow along with the example code, clone the repository and go to the
$ git clone https://github.com/smallstep/certificates.git Cloning into 'certificates'... remote: Enumerating objects: 16, done. remote: Counting objects: 100% (16/16), done. remote: Compressing objects: 100% (15/15), done. remote: Total 8355 (delta 3), reused 5 (delta 0), pack-reused 8339 Receiving objects: 100% (8355/8355), 34.92 MiB | 11.05 MiB/s, done. Resolving deltas: 100% (5727/5727), done. $ cd ./certificates/examples/basic-federation
Open two terminals to use as online CAs and call them
Cloud CA and
Kubernetes CA. The password for both of these online CAs is
$ step-ca ./pki/cloud/config/ca.federated.json Please enter the password to decrypt intermediate_ca_key: password 2019/01/22 13:38:52 Serving HTTPS on :1443 ...
$ step-ca ./pki/kubernetes/config/ca.federated.json Please enter the password to decrypt intermediate_ca_key: password 2019/01/22 13:39:44 Serving HTTPS on :2443 ...
Notice the difference between the two configuration options below.
Cloud CA will list
Kubernetes CA in the
federatedRoots section and vice versa.
$ diff pki/cloud/config/ca.json pki/cloud/config/ca.federated.json 3c3 "federatedRoots": , "federatedRoots": ["pki/cloud/certs/kubernetes_root_ca.crt"],
Bringing up the demo server
Once both online CAs are up and running, let's bring up the demo server, using
a certificate from the
Cloud CA. This demo server leverages step's
SDK to obtain X.509
certificates, automatically renew them, and fetch a trusted roots bundle. When
it starts, it will report what root certificates it will use to authenticate
$ go run server/main.go $(step ca token --ca-url https://localhost:1443 --root ./pki/cloud/certs/root_ca.crt 127.0.0.1) ✔ Key ID: EE1ZiqkMaxsUdpz8SCSkRBzwK9TWUoidQnMnJ8Eryn8 (email@example.com) ✔ Please enter the password to decrypt the provisioner key: password Server is using federated root certificates Accepting certs anchored in CN=Smallstep Public Cloud Root CA Accepting certs anchored in CN=Smallstep Kubernetes Root CA Listening on :8443 ...
Running the demo client
Similarly, step's SDK provides a client option to mutually authenticate connections to servers. It automatically handles certificate bootstrapping, renewal, and fetches a bundle of trusted roots. The demo client will send HTTP requests to the demo server periodically or about every 5s. This client is going to use a certificate from the
$ go run client/main.go $(step ca token sdk_client --ca-url https://localhost:2443 --root ./pki/kubernetes/certs/root_ca.crt) ✔ Key ID: S5gYgpeqcIAgc1Zr4myZXpgJ_Ao4ryS6F6wqg9o8RYo (firstname.lastname@example.org) ✔ Please enter the password to decrypt the provisioner key: password Server responded: Hello sdk_client (cert issued by 'Smallstep Kubernetes Root CA') at 2019-01-23 00:51:38.576648 +0000 UTC
Curl as a client
While the demo client provides a convenient way to periodically send requests to the demo server, curl in combination with a client certificate from
Kubernetes CA can hit the server instead:
$ step ca certificate kube_client kube_client.crt kube_client.key --ca-url https://localhost:2443 --root pki/kubernetes/certs/root_ca.crt ✔ Key ID: S5gYgpeqcIAgc1Zr4myZXpgJ_Ao4ryS6F6wqg9o8RYo (email@example.com) ✔ Please enter the password to decrypt the provisioner key: ✔ CA: https://localhost:2443/1.0/sign ✔ Certificate: kube_client.crt ✔ Private Key: kube_client.key
Federation relies on a bundle of multiple trusted roots which need to be fetched before being passed into curl.
$ step ca federation --ca-url https://localhost:1443 --root pki/cloud/certs/root_ca.crt federated.pem The federation certificate bundle has been saved in federated.pem.
Then you have to pass the certificate issued by Kubernetes CA into curl using the appropriate command line flags:
$ curl -i --cacert federated.pem --cert kube_client.crt --key kube_client.key https://127.0.0.1:8443 HTTP/1.1 200 OK Date: Mon, 28 Jan 2019 15:24:54 GMT Content-Type: text/plain; charset=utf-8 Content-Length: 105 Hello kube_client (cert issued by 'Smallstep Kubernetes Root CA') at 2019-01-28 15:24:54.864373 +0000 UTC
Since the demo server is enrolled with the federated
Cloud CA that trusts
X.509 certificates issued by the
Kubernetes CA through federation, the connection
is successfully established.