Impersonation Webhook

This admission webhook supports impersonation feature provided by Razee controllers by intercepting requests that create razee resources (such as RemoteResource and MustacheTemplate) and updates the spec.clusterAuth.impersonateUser field accordingly based on the following rules:

| | impersonateUser set | impersonateUser not set | | ---| --- | --- | |The authenticated can impersonate|not changed|authenticated user| |The authenticated cannot impersonate|authenticated user|authenticated user|

Note: "user" implies normal users or service accounts, whichever applicable.

The webhook relies on the authorization.k8s.io API group, specifically SubjectAccessReview API, to determine the authenticated user's permission. Refer to role-based access control and checking-api-access for more information.

Since this webhook has already performed the validation, downstream razee controllers will respect clusterAuth.impersonateUser value and impersonate the specified user.

Installation

Razee Deploy Delta is the recommended way to install this webhook.

Communication between admission controllers and webhooks is via HTTPS:

• Webhook servers must present a valid certificate. The certificate and key are stored in impersonation secret.
• Admission controllers will validate the presented certificate by using the certificate authority set in caBundle field in impersonation-webhook MutatingWebhookConfiguration.

Note: Razee Deploy Delta will deploy the webhook with a self-signed certificate by default. Custom certificate can be used by updating impersonation secret and impersonation-webhook MutatingWebhookConfiguration.

For your reference, a self-signed certificate can be quickly created with the following command for demo purpose:

openssl req -x509 -newkey rsa:4096 -sha256 -days 3650 -nodes -keyout server.key 
-out server.crt -subj "/CN=impersonation-webhook.{NAMESPACE}.svc" 
-addext "subjectAltName=DNS:impersonation-webhook.{NAMESPACE}.svc"

Customize the webhook

The optional razeedeploy-config ConfigMap can be used to customize the webhook.

Because the ConfigMap is optional, if it is created after the ImpersonationWebhook deployment, you must restart ImpersonationWebhook deployment's pods, so the deployment can mount the ConfigMap as a volume.

Example:

apiVersion: v1
kind: ConfigMap
metadata:
  name: razeedeploy-config
  namespace: razee
data:
  enable-impersonation: "false"

Enable User Impersonation

With enable-impersonation set to "false" (default), the webhook will not perform permission validation.

Impersonation with Nested Resources

It is possible to have a deployment with multiple nested resources like this:

RemoteResource 1:
  - impersonate user: B
  - download: RemoteResource 2

RemoteResource 2:
  - impersonate user: C
  - download: A K8 deployment

Assume A creates RemoteResource 1. If A has impersonation permission, RemoteResource 2 will be created under the name of user B (it's equivalent to that B creates RemoteResource 2). Otherwise, it will be created under the name of user A.

Assume A has impersonation permission, RemoteResource 2 will be created under the name of user B. Recursively, if B has impersonation permission, the K8 deployment will be created under the name of user C. Otherwise, it will be created under the name of B.

In this case, users should be aware of this impersonation process and make sure that necessary role bindings are created to achieve desired outcome. The webhook relies on the authorization.k8s.io API group, specifically SubjectAccessReview API, to determine a user's permission.