Automatically generated secrets for Kubernetes

This repository contains a custom Kubernetes controller that can automatically create random secret values. This may be used for auto-generating random credentials for applications run on Kubernetes.

Security note

Older versions (<= 1.0.0) of this controller used the math/rand package for generating secrets, which is deterministic and not cryptographically secure (see #1 for more information). If you're already running this controller and want to regenerate all potentially compromised secrets, start the controller with the -regenerate-insecure flag (note that you will need to manually re-create any Pods using these secrets, though). When using the kubectl apply command from below, the new flag will be added to your Deployment automatically.

Deployment

Helm

The controller can be deployed using Helm.

You might want to take a look a the values.yaml to adjust the operator to your needs:

• secretLength defines the length of the generated secret values.

• watchNamespace defines, which namespaces should be watched for secret objects.

• useMetricsService toggles whether the operator should provide a service for metrics monitoring by Prometheus. If this is set to true, the operator will start with additional permissions, namely get permissions for replicasets and deployments in the apiGroup apps, as well as create permissions for services and create the needed services during startup.

  To watch a single namespace, set it to the desired namespace name. Multiple namespaces are supported and can be set as a comma-separated list: ns1,ns2.

  If watchNamespace is set to the empty string value "", all namespaces will be watched.

• rbac.create controls if rbac resources are deployed.

• rbac.clusterRole controls if secrets generator has permission to watch secrets in namespaces other than where it has been deployed.

  rbac.clusterRole=false & watchNamespace="" will result in watchNamespace being set to the current namespace as this is all the permissions will allow access to.

Afterwards, deploy the operator using:

1. Add the Mittwald Charts Repo:

   $ helm repo add mittwald https://helm.mittwald.de
   "mittwald" has been added to your repositories
   
   $ helm repo update
   Hang tight while we grab the latest from your chart repositories...
   ...Successfully got an update from the "mittwald" chart repository
   Update Complete. ⎈ Happy Helming!⎈

2. Upgrade or install kubernetes-secret-generator:

   $ helm upgrade --install kubernetes-secret-generator mittwald/kubernetes-secret-generator

Manually

If you don't want to use Helm (why wouldn't you?), the required .yaml files can also be applied manually using kubectl apply:

$ make install

To uninstall, use:

$ make uninstall

Usage

This operator is capable of generating secure random strings and ssh keypair secrets.

It supports two ways of secret generation, annotation-based and cr-based.

Annotation-based generation

For annotation based generation, the type of secret to be generated can be specified by the secret-generator.v1.mittwald.de/type annotation. This annotation can be added to any Kubernetes secret object in the operators watchNamespace.

The encoding of the secret can be specified by the secret-generator.v1.mittwald.de/encoding annotation. Available encodings are base64, base64url, base32, hex and raw, with raw returning the unencoded byte sequence that was generated. base64 will be used, if the annotation was not used.

The length of the generated secret can be specified by the secret-generator.v1.mittwald.de/length annotation. By default, this length refers to the length of the generated string, and not the length of the byte sequence encoded by it. The suffix B or b can be used to indicate that the provided value should refer to the encoded byte sequence instead.

Secure Random Strings

By default, the operator will generate secure random strings. If the type annotation is not present, it will be added after the first reconciliation loop and its value will be set to string.

To actually generate random string secrets, the secret-generator.v1.mittwald.de/autogenerate annotation is required as well. The value of the annotation can be a field name (or comma separated list of field names) within the secret; the SecretGeneratorController will pick up this annotation and add a field [or fields] (password in the example below) to the secret with a randomly generated string value.

apiVersion: v1
kind: Secret
metadata:
  name: string-secret
  annotations:
    secret-generator.v1.mittwald.de/autogenerate: password
data:
  username: c29tZXVzZXI=

after reconciliation:

apiVersion: v1
kind: Secret
metadata:
  name: string-secret
  annotations:
    secret-generator.v1.mittwald.de/type: string
    secret-generator.v1.mittwald.de/secure: "yes"
    secret-generator.v1.mittwald.de/autogenerate: password
    secret-generator.v1.mittwald.de/autogenerate-generated-at: "2020-04-03T14:07:47+02:00"
type: Opaque
data:
  username: c29tZXVzZXI=
  password: TWVwSU83L2huNXBralNTMHFwU3VKSkkwNmN4NmRpNTBBcVpuVDlLOQ==

SSH Key Pairs

To generate SSH Key Pairs, the secret-generator.v1.mittwald.de/type annotation has to be present on the kubernetes secret object.

The operator will then add two keys to the secret object, ssh-publickey and ssh-privatekey, each containing the respective key.

The Private Key will be PEM encoded, the Public Key will have the authorized-keys format.

apiVersion: v1
kind: Secret
metadata:
  annotations:
    secret-generator.v1.mittwald.de/type: ssh-keypair
data: {}

after reconciliation:

apiVersion: v1
kind: Secret
metadata:
  annotations:
    secret-generator.v1.mittwald.de/type: ssh-keypair
    secret-generator.v1.mittwald.de/autogenerate-generated-at: "2020-04-03T14:07:47+02:00"
type: Opaque
data:
  ssh-publickey: c3NoLXJzYSBBQUFBQ...
  ssh-privatekey: LS0tLS1CRUdJTi...

Ingress Basic Auth

To generate Ingress Basic Auth credentials, the secret-generator.v1.mittwald.de/type annotation has to be present on the kubernetes secret object.

The operator will then add three keys to the secret object. The ingress will interpret the auth key as a htpasswd entry. This entry contains the username, and the hashed generated password for the user. The operator also stores the username and cleartext password in the username and password keys.

If a username other than admin is desired, it can be specified using the secret-generator.v1.mittwald.de/basic-auth-username annotation.

apiVersion: v1
kind: Secret
metadata:
  annotations:
    secret-generator.v1.mittwald.de/type: basic-auth
data: {}

after reconciliation:

apiVersion: v1
kind: Secret
metadata:
  annotations:
    secret-generator.v1.mittwald.de/type: basic-auth
    secret-generator.v1.mittwald.de/autogenerate-generated-at: "2020-04-03T14:07:47+02:00"
type: Opaque
data:
  username: admin
  password: test123
  auth: "admin:PASSWORD_HASH"

CR-based generation

The operator supports three kinds of custom resources: StringSecret, SSHKeyPair and BasicAuth. These crs can be used to trigger creation, update and deletion of desired secrets. All crs support the field spec.type which can be used to define the kubernetes type of the generated Secret, e.g. "Opaque"

Secure Random Strings via StringSecret-CR

A StringSecret resource can be used to generate secure random strings similar to the ones offered by the annotation approach. Desired Fields to be randomly generated can be supplied via the spec.fields property, which can be used to specify a list of fields with individual encoding and length values, e.g. a hex-encoded string of length 15 and a base64-encoded string of length 40 can be defined in the same secret object. The spec.data property can be used to specify arbitrary data entries the generated secret's data property should be populated with. Finally, the spec.forceRegenerate property can be used to control regeneration of secret fields.

Example:

apiVersion: "secretgenerator.mittwald.de/v1alpha1"
kind: "StringSecret"
metadata:
  name: "example-pw"
  namespace: "default"
spec:
  forceRegenerate: false
  data:
    username: "testuser"
  fields:
    - fieldName: "test"
      encoding: "hex"
      length: "15"

Upon creation of the cr, the controller will attempt to create a Secret resource matching the specifications. If successful, the new resource will have its owner set as the StringSecret used to create it, providing automated deletion/updating of the secret if the creating cr is deleted/updated. The StringSecret will store an object reference to the created Secret in its status field. During updating, any new fields in spec.data and spec.fields will be added, while existing fields will only be overwritten/regenerated if spec.forceRegenerate is set to true. If the target Secret already exists and is not owned by a StringSecret resource, no changes will be made to ìt.

SSH Key Pair via SSHKeyPair-CR

A SSHKeyPair resource can be used to generate an ssh key pair. It supports spec.length, spec.data and spec.forceRegenerate similar to StringSecret resources. The field spec.privateKey can be used to specify a private key, which will be used during runtime to regenerate a matching public key. Updating is handled similar to StringSecret resources, unowned Secrets are not modified, and existing fields are only updated if regeneration is forced. However, should the public key be missing, the operator will attempt to regenerate it.

apiVersion: "secretgenerator.mittwald.de/v1alpha1"
kind: "SSHKeyPair"
metadata:
  name: "example-ssh"
  namespace: "default"
spec:
  length: "40"
  forceRegenerate: false
  data:
    example: "data"

Ingress Basic Auth via BasicAuth-CR

A BasicAuth resource can be used to generate Ingress Basic Auth credentials. Supported properties are spec.length, spec.encoding, spec.data and spec.forceRegenerate. To specify a username, use spec.username. If no username is provided, the operator will use admin. Updates follow the same rules as for the other crs, existing secrets will only be updated if owned by a BasicAuth resource and if spec.forceRegenerate is set to true. The exception to this are new spec.data entries, which are added even if forceRegenerate is false, and cases where the auth field in the Secret is empty.

apiVersion: "secretgenerator.mittwald.de/v1alpha1"
kind: "BasicAuth"
metadata:
  name: "example-auth"
  namespace: "default"
spec:
  length: "40"
  username: "testuser"
  encoding: "base64"
  forceRegenerate: false
  data:
    example: "data"

Operational tasks

• Regenerate all automatically generated secrets:

  $ kubectl annotate secrets --all secret-generator.v1.mittwald.de/regenerate=true
  

• Regenerate only certain fields, in case the secret is of the password type:

  $ kubectl annotate secrets --all secret-generator.v1.mittwald.de/regenerate=password1,password2