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Cloud Foundry (CF) auth method

Note: This engine can use external X.509 certificates as part of TLS or signature validation. Verifying signatures against X.509 certificates that use SHA-1 is deprecated and is no longer usable without a workaround starting in Vault 1.12. See the deprecation FAQ for more information.

The cf auth method provides an automated mechanism to retrieve a Vault token for CF instances. It leverages CF's App and Container Identity Assurance. At a high level, this works as follows:

  1. You construct a request to Vault including your CF_INSTANCE_CERT, signed by your CF_INSTANCE_KEY.
  2. Vault validates that the signature is no more than 300 seconds old, or 60 seconds in the future.
  3. Vault validates that the cert was issued by the CA certificate you've pre-configured.
  4. Vault validates that the request was signed by the private key for the CF_INSTANCE_CERT.
  5. Vault validates that the CF_INSTANCE_CERT application ID, space ID, and org ID presently exist.
  6. If all checks pass, Vault issues an appropriately-scoped token.

Known risks

This authentication engine uses CF's instance identity service to authenticate users to Vault. Because CF makes its CA certificate and private key available to certain users at any time, it's possible for someone with access to them to self-issue identity certificates that meet the criteria for a Vault role, allowing them to gain unintended access to Vault.

For this reason, we recommend that if you enable this auth method, you carefully guard access to the private key for your instance identity CA certificate. In CredHub, it can be obtained through the following call: $ credhub get -n /cf/diego-instance-identity-root-ca.

Take extra steps to limit access to that path in CredHub, whether it be through use of CredHub's ACL system, or through carefully limiting the users who can access CredHub.

Usage

Preparing to configure the plugin

To configure this plugin, you'll need to gather the CA certificate that CF uses to issue each CF_INSTANCE_CERT, and you'll need to configure it to access the CF API.

To gain your instance identity CA certificate, in the cf dev environment it can be found using:

$ bosh int --path /diego_instance_identity_ca ~/.cfdev/state/bosh/creds.yml

In environments containing Ops Manager, it can be found in CredHub. To gain access to CredHub, first install the PCF command-line utility and authenticate to it using the metadata file it describes. These instructions also use jq for ease of drilling into the particular part of the response you'll need.

Once those steps are complete, get the credentials you'll use for CredHub:

$ pcf settings | jq '.products[0].director_credhub_client_credentials'

SSH into your Ops Manager VM:

$ ssh -i ops_mgr.pem ubuntu@$OPS_MGR_URL

Please note that the above OPS_MGR_URL shouldn't be prepended with https://.

Log into CredHub with the credentials you obtained earlier:

$ credhub login --client-name=director_to_credhub --client-secret=some-secret

And view the root certificate CF uses to issue instance identity certificates:

$ credhub get -n /cf/diego-instance-identity-root-ca

The output to that call will include two certificates and one RSA key. You will need to copy the certificate under ca: | and place it into a file on your local machine that's properly formatted. Here's an example of a properly formatted CA certificate:

$ cat ca.crt
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

An easy way to verify that your CA certificate is properly formatted is using OpenSSL like so:

$ openssl x509 -in ca.crt -text -noout
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            3e:a4:f2:d6:ab:df:1c:d1:15:bb:1b:25:f6:5d:60:95:8f:39:39
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN=Diego Instance Identity Root CA
        Validity
            Not Before: Jun  6 09:12:01 2019 GMT
            Not After : Jun  5 09:12:01 2022 GMT
        Subject: CN=Diego Instance Identity Root CA
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:b6:bc:c4:60:d8:4f:fa:b7:53:31:0a:02:c2:c3:
                    6a:38:6e:1f:13:e9:20:f1:65:09:7c:29:ea:ef:14:
                    e5:0a:df:e3:6e:d7:a1:fe:e7:ad:74:4a:cd:1b:b7:
                    83:b1:36:d1:4f:ce:c3:38:01:8b:75:59:b3:c4:f6:
                    f4:91:8d:59:e0:36:93:41:ed:5f:ca:10:f9:67:3c:
                    42:78:33:f4:cf:2d:d6:1f:52:66:5c:79:7c:67:f1:
                    3e:dd:f1:ef:1a:33:68:81:89:f2:9e:07:29:01:f5:
                    66:58:ab:2f:b7:73:ba:7e:d8:fb:b9:ba:13:2f:1c:
                    31:5b:1e:a6:a5:2c:eb:8a:fc:f8:aa:42:6f:12:89:
                    ad:5d:38:aa:d4:cd:96:bd:0b:1b:7c:8e:c5:21:e5:
                    8a:9f:83:0e:f5:15:2f:78:d2:17:3f:c9:0d:6c:70:
                    0b:29:a2:14:10:21:d1:08:c6:d4:b2:a9:d8:58:ac:
                    51:1a:17:19:8f:87:25:b7:f6:4a:da:4a:de:2e:1d:
                    62:7c:50:5d:09:4c:0e:98:a9:a3:32:bb:58:5c:6f:
                    de:01:f8:43:a6:0c:66:f9:66:20:f8:9d:00:5f:05:
                    c5:f0:c8:b1:87:2a:4e:04:39:ab:4a:6b:f6:66:ee:
                    f2:82:9b:67:be:2f:c9:93:2a:8b:2f:ab:f6:f2:e1:
                    6e:ed
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Subject Key Identifier:
                01:DF:A7:0A:81:85:9F:3F:03:A6:40:BD:4F:A9:E4:93:F3:FE:89:A3
            X509v3 Authority Key Identifier:
                keyid:01:DF:A7:0A:81:85:9F:3F:03:A6:40:BD:4F:A9:E4:93:F3:FE:89:A3

            X509v3 Basic Constraints: critical
                CA:TRUE
    Signature Algorithm: sha256WithRSAEncryption
         3b:83:25:eb:fe:e9:b3:82:bf:bb:7d:49:2e:0d:77:fc:de:44:
         4b:85:f4:82:ac:1c:31:eb:61:46:41:20:ed:5a:05:06:ce:3b:
         58:83:b4:be:15:03:72:c1:13:1e:9f:3a:03:79:7d:bc:6b:a1:
         4b:33:5f:df:fa:3e:dc:4b:7b:ee:54:f2:2e:4c:3b:3b:4a:f8:
         ec:71:3e:bb:43:7e:76:e5:5d:56:fa:21:6e:04:2a:14:e7:59:
         eb:12:ed:1d:96:9c:e5:ad:ce:a4:50:5c:a1:54:be:80:67:dd:
         07:24:2d:5d:68:f5:ea:b3:60:81:3f:6a:86:f8:cf:41:9a:55:
         a9:c0:f4:f4:b3:cd:b5:4f:b1:7e:fd:44:20:f5:07:b3:66:57:
         47:0a:11:0e:c8:ac:2a:e1:2f:b1:25:0d:5f:c6:94:da:ed:55:
         d1:e3:63:49:b0:cf:d8:ae:fb:46:09:bf:1b:dc:1c:34:c4:46:
         2d:74:e9:bd:bc:29:7c:c9:cf:e3:f9:fe:1c:a0:db:0a:91:5f:
         37:48:7d:a5:c0:8d:6d:24:ba:ae:67:c7:22:54:00:bc:31:0f:
         ff:29:cf:be:ee:36:de:30:e9:67:c9:a1:20:cc:e9:7a:c0:22:
         18:75:e4:ad:ed:66:0f:44:cc:19:80:67:fe:43:8c:ad:11:72:
         60:b2:69:7c

You will also need to configure access to the CF API. To prepare for this, we will now use the cf command-line tool.

First, while in the directory containing the metadata file you used earlier to authenticate to CF, run $ pcf target. This points the cf tool at the same place as the pcf tool. Next, run $ cf api to view the API endpoint that Vault will use.

Next, configure a user for Vault to use. This plugin was tested with Org Manager level permissions, but lower level permissions may be usable.

$ cf create-user vault pa55w0rd
$ cf orgs
$ cf org-users my-example-org
$ cf set-org-role vault my-example-org OrgManager

Specifically, the vault user created here will need to be able to perform the following API calls:

  • Method: "GET", endpoint: "/v2/info"
  • Method: "POST", endpoint: "/oauth/token"
  • Method: "GET", endpoint: "/v2/apps/\$APP_ID"
  • Method: "GET", endpoint: "/v2/organizations/\$ORG_ID"
  • Method: "GET", endpoint: "/v2/spaces/\$SPACE_ID"

Next, PCF often uses a self-signed certificate for TLS, which can be rejected at first with an error like:

x509: certificate signed by unknown authority

If you encounter this error, you will need to first gain a copy of the certificate that CF is using for the API via:

$ openssl s_client -showcerts -servername domain.com -connect domain.com:443

Here is an example of a real call:

$ openssl s_client -showcerts -servername api.sys.somewhere.cf-app.com -connect api.sys.somewhere.cf-app.com:443

Part of the response will contain a certificate, which you'll need to copy and paste to a well-formatted local file. Please see ca.crt above for an example of how the certificate should look, and how to verify it can be parsed using openssl. The walkthrough below presumes you name this file cfapi.crt.

Walkthrough

After obtaining the information described above, a Vault operator will configure the CF auth method like so:

$ vault auth enable cf

$ vault write auth/cf/config \
      identity_ca_certificates=@ca.crt \
      cf_api_addr=https://api.dev.cfdev.sh \
      cf_username=vault \
      cf_password=pa55w0rd \
      cf_api_trusted_certificates=@cfapi.crt

$ vault write auth/cf/roles/my-role \
    bound_application_ids=2d3e834a-3a25-4591-974c-fa5626d5d0a1 \
    bound_space_ids=3d2eba6b-ef19-44d5-91dd-1975b0db5cc9 \
    bound_organization_ids=34a878d0-c2f9-4521-ba73-a9f664e82c7bf \
    policies=my-policy

Once configured, from a CF instance containing real values for the CF_INSTANCE_CERT and CF_INSTANCE_KEY, login can be performed using:

$ vault login -method=cf role=test-role

For CF, we do also offer an agent that, once configured, can be used to obtain a Vault token on your behalf.

Enabling mutual TLS with the CF API

The CF API can be configured to require mutual TLS with clients. This plugin supports mutual TLS by setting the cf_api_mutual_tls_certificate and cf_api_mutual_tls_key configuration properties.

$ vault write auth/cf/config \
      identity_ca_certificates=@ca.crt \
      cf_api_addr=https://api.dev.cfdev.sh \
      cf_username=vault \
      cf_password=pa55w0rd \
      cf_api_trusted_certificates=@cfapi.crt \
      cf_api_mutual_tls_certificate=@cfmutualtls.crt \
      cf_api_mutual_tls_key=@cfmutualtls.key

The provided certificate must be signed by a certificate authority trusted by the CF API. Obtaining such a certificate depends on the specifics of your deployment of Cloud Foundry.

Maintenance

In testing we found that CF instance identity CA certificates were set to expire in 3 years. Some CF docs indicate they expire every 4 years. However long they last, at some point you may need to add another CA certificate - one that's soon to expire, and one that is currently or soon-to-be valid.

$ CURRENT=$(cat /path/to/current-ca.crt)
$ FUTURE=$(cat /path/to/future-ca.crt)
$ vault write auth/vault-plugin-auth-cf/config identity_ca_certificates="$CURRENT" identity_ca_certificates="$FUTURE"

If Vault receives a CF_INSTANCE_CERT matching any of the identity_ca_certificates, the instance cert will be considered valid.

A similar approach can be taken to update the cf_api_trusted_certificates.

Troubleshooting At-A-Glance

If you receive an error containing x509: certificate signed by unknown authority, set cf_api_trusted_certificates as described above.

If you're unable to authenticate using the CF_INSTANCE_CERT, first obtain a current copy of your CF_INSTANCE_CERT and copy it to your local environment. Then divide it into two files, each being a distinct certificate. The first certificate tends to be the actual identity.crt, and the second one tends to be the intermediate.crt. Verify each are properly named and formatted using a command like:

$ openssl x509 -in ca.crt -text -noout

Then, verify that the certificates are properly chained to the ca.crt you've configured:

$ openssl verify -CAfile ca.crt -untrusted intermediate.crt identity.crt

This should show a success response. If it doesn't, try to identify the root cause, be it an expired certificate, an incorrect ca.crt, or a Vault configuration that doesn't match the certificates you're checking.

API

The CF auth method has a full HTTP API. Please see the CF Auth API for more details.

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