Using Vault as a Certificate Authority

Using Vault as a Certificate Authority

For the next few weeks we are doing a POC on Hashicorp’s Vault. While I am still learning about all of the functionality that Vault provides, there are a few key pieces I have already identified to check out in addition to just storing credentials. One of the big ones is the PKI backend. This would make it a lot easier for not just my team, but developers as well to generate SSL certificates. While I found some basic instructions on how to set it up from various sources (mentioned later), I decided to do my own write-up that would consolidate everything I learned.

Create the Root and Intermediate Certificates

Rather than writing up instructions on how to create a the root or intermediate CA’s, I will just post the instructions that I followed that were written up by Jamie Nguyen entitled OpenSSL Certificate Authority. For the purposes of this document, I followed the sections called Create the root pair and Create the intermediate pair.

It’s also possible to create a root certificate authority (and/or an intermediary certificate), but I prefer to do this outside of Vault so that my root certificate remains secure.

Initialize the PKI Backend

Once you have your root and intermediate certificates generated, the first think that you want to do is prepare them for upload to Vault. You can do that with by combining the intermediate certificate with your key.

cat intermediate/certs/ca-chain.cert.pem > /tmp/ca_bundle.pem
openssl rsa -in intermediate/private/intermediateCA.key.pem >> /tmp/ca_bundle.pem

These two commands will concatenate everything into one file called ca_bundle.pem. The next step is to initialize and configure the PKI backend. I was able to find some pretty good instructions on configuring it between Cuddletech’s website and a post by Joel Bastos. But since most of what I want to use Vault for will be driven from automation, I decide to focus on utilizing only the API (which made things just a little tougher).

The first step is to initialize some environmental variables that will make our commands easier to run. You’ll want to set the VAULT_ADDR to your URL of your vault server and VAULT_TOKEN to your login token.

export VAULT_ADDR=vault.example.com:8200
export VAULT_TOKEN=a38dc275-86d3-48bd-57ae-237a45d6663b

Once set, you can test your configuration using the curl command to go to the health endpoint.

% curl -k -X GET ${VAULT_ADDR}/v1/sys/health
{"initialized":true,"sealed":false,"standby":false,"server_time_utc":1477441389,"version":"0.6.2","cluster_name":"vault-cluster-2fbd0333","cluster_id":"d8056c7f-acbb-ae59-4ed4-3673f2d27d48"}

Configure the PKI Backend

After you have verified that the endpoint works, you can create and configure your PKI backend.

curl -k -X POST-H "x-Vault-Token: ${VAULT_TOKEN}" -d '{"type": "pki",   "description": "Test Root CA", "config": { "max_lease_ttl":     "87600h"}}'  ${VAULT_ADDR}/v1/sys/mounts/pki-test

This command creates a new PKI backend mount called “pki-test” and sets the max_lease_ttl to 10 years. You may want to adjust these settings to whatever is suitable for your environment.
Since the post doesn’t return anything, you can verify it with the mounts endpoint. If you don’t have jq, I highly recommend you download it, as it makes viewing JSON output much easier

curl -k -X GET -H "x-Vault-Token: ${VAULT_TOKEN}" ${VAULT_ADDR}/v1/sys/mounts|jq .

Once you have initialized the backend, you can upload the certificate bundle that you created by following the instructions noted above.

curl -k -X POST -H "x-Vault-Token: ${VAULT_TOKEN}" -d @<(jq -n --arg a "$(</tmp/ca_bundle.pem)" '{ pem_bundle: $a }') ${VAULT_ADDR}/v1/pki-test/config/ca

This command doesn’t return anything either. You can verify that it uploaded properly by trying to download the intermediate certificate.

curl -k -X GET -H "x-Vault-Token: ${VAULT_TOKEN}" ${VAULT_ADDR}/v1/pki-test/ca/pem

Create a Role

The final step is to configure a role to issue the certificates.

curl -k -X POST -H "x-Vault-Token: ${VAULT_TOKEN}" -d '{"allow_any_name": "true", "allow_ip_sans": "true", "max_ttl": "17520h"}' ${VAULT_ADDR}/v1/pki-test/roles/example-dot-com

You can verify that the role exists with a GET to the roles endpoint.

curl -k -X GET -H "x-Vault-Token: ${VAULT_TOKEN}" ${VAULT_ADDR}/v1/pki-test/roles/example-dot-com|jq .

Issue Certificates

Now we are all set to issue certificates from our Vault server. This can be done one of two ways. The first is to request a certificate and key from the Vault directly:

curl -H "X-Vault-Token: ${VAULT_TOKEN}"   -d '{ "common_name": "testhost.example.com" }' https://${VAULT_ADDR}/v1/pki-test/issue/example-dot-com | tee >(jq -r .data.certificate > test.example.com.cert) >(jq -r .data.private_key > test.example.com.pem) >(jq -r .data.ca_chain[] > test.example.com-chained.pem)

This will create three files in your directory, one that contains the key, one that contains the certificate, and one that contains the certificate chain. You can also send a CSR that you created to have a certificate generated.

curl -k -X POST -H "X-Vault-Token: ${VAULT_TOKEN}" -d @<(jq -n --arg a "test.example.com" --arg b "$(<../server.csr)" '{ common_name: $a, csr: $b }') ${VAULT_ADDR}/v1/pki-test/sign/example-dot-com| tee >(jq -r .data.certificate > test.example.com.cert) >(jq -r .data.ca_chain[] > test.example.com-chained.pem)

Since the key was generated separately, it won’t create a new key file, but it does generate the certificate file and the certificate chain.

That’s all it takes to get a functioning CA in Vault. I’m sure that I still have a whole lot to learn about configuring and securing the PKI backend, but for our POC I think this will work nicely.

Comments are closed.