/credhub-service-broker

Keep app secrets safe from `cf env` by storing them in Credhub

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credhub-service-broker

This is a Cloud Foundry service broker allowing users to store app secrets in CredHub. That offers more effective security and auditing than storing secrets in Cloud Controller.

Secrets stored in app environment variables (cf set-env) or in user-provided services (cf cups) can be seen in cf env or /v2/app/:guid responses. Auditing of those endpoints is ineffective (they have many regular legitimate uses.)

When using this service broker, secrets should only be accessible by:

  • SSHing into an app, generating CC Audit Events

  • accessing CredHub, generating CredHub Audit Events

  • having the app print them out, which can be mitigated by code review

  • compromising the platform or the app

Usage

Here's an example of how to use it to provide AWS credentials to apps:

$ cf create-service secrets simple aws-secrets \
    -c '{"AWS_ACCESS_KEY_ID": "…", "AWS_SECRET_ACCESS_KEY": "…", […]}'

$ cf push first-app-using-aws-creds --no-start
$ cf bind-service first-app-using-aws-creds aws-secrets
$ cf start first-app-using-aws-creds

$ cf push second-app-using-aws-creds --no-start
$ cf bind-service second-app-using-aws-creds aws-secrets
$ cf start second-app-using-aws-creds

If you run cf env against those apps you don't get back anything sensitive:

VCAP_SERVICES='{
  "secrets": [{
    "credentials": {
      "credhub-ref": "non-sensitive-string"
    }
  }]
}'

The value of credhub-ref is only useful if you already have access to CredHub, and CredHub access can be audited well.

Cloud Foundry retrieves the credentials from CredHub when the apps start, without any changes needed to your app. The app sees the proper AWS credentials in VCAP_SERVICES:

VCAP_SERVICES='{
  "secrets": [{
    "credentials": {
      "AWS_ACCESS_KEY_ID": "AZ…"
      "AWS_SECRET_ACCESS_KEY": "Zy…",
      […]
    }
  }]
}'

As usual for CF apps your app can either parse the VCAP_SERVICES environment variable or use something like the env-map-buildpack to do it for you at app startup.

Installation

First your Cloud Foundry deployment has to be able to support this:

  • You need to have enabled CredHub in your Cloud Foundry deployment
  • You need to have configured a credhub link to Cloud Controller in your BOSH manifest
  • You need to allow traffic from all apps to the VMs hosting CredHub, for instance by adding the appropriate CF Security Groups
  • You need to allow the credhub-service-broker app to talk to your CredHub, UAA and Locket
  • There is an example of how we did some of this for our Cloud Foundry deployment: commit 5761b8df on github.com/alphagov/paas-cf

Once all that is done you need to collect quite a few configuration variables. Make a copy of blank-vars-store.yml and fill it out with values for your Cloud Foundry deployment. Then try deploying it:

$ cf push --vars-file vars-store.yml

$ cf create-service-broker \
    credhub-broker \
    BASIC-AUTH-USERNAME-FROM-VARS-FILE \
    BASIC-AUTH-PASSWORD-FROM-VARS-FILE \
    ROUTE-FROM-VARS-FILE

$ cf enable-service-access -b credhub-broker

If the configuration works you should now be able to follow the usage examples further up this document.

So far there are no acceptance or smoke tests. Those will come later if this project gets adopted.

Future direction

So far this broker re-uses existing Cloud Foundry features created for Pivotal's closed-source CredHub Service Broker. However that comes with some big limitations that prevent our users from taking full advantage of CredHub's automation (e.g., acting as a CA.) In future we could grant our users directly access to Credhub so they can manage secrets with Terraform or similar. We could also support the credhub-buildpack to allow more flexible use of secrets.