RBAC Authorization Overview

Authentication

In Kubernetes, you must be authenticated (logged in) before your request can be authorized (granted permission to access). The same applies to the Web UI of StackGres, you can create users to authenticate against a Kubernetes using a special Secret designed for that purpose to log in in the Web UI.

The data that contains the secret must be in base64 format, and the password should be the concatenation of the api username plus the password itself.

apiVersion: v1
kind: Secret
metadata:
  name: webapi-user-demo
  namespace: stackgres
  labels:
    api.stackgres.io/auth: user
type: Opaque
data:
  apiUsername: "demo@example.com | b64enc"
  k8sUsername: "username | b64enc"
  password: "{{ user + password | sha256sum | b64enc }}"

You might wonder why are two username fields in the secret, the apiUsername is optional and is used to “customize” the username used for the login Web UI, the k8sUsername is the username that is used to impersonate the API calls to K8s.

Using RBAC Authorization

Role-based access control (RBAC) is a method of regulating access to computer or network resources based on the roles of individual users within your organization.

RBAC authorization uses the rbac.authorization.k8s.io API group to drive authorization decisions, allowing you to dynamically configure policies through the Kubernetes API.

Kubernetes supports others authorizations modes like Attribute-based access control (ABAC), but the RBAC mode must be enabled in Kubernetes for this to work.

Kubernetes authorizes API requests using the API server. It evaluates all of the request attributes against all policies and allows or denies the request. All parts of an API request must be allowed by some policy in order to proceed. This means that permissions are denied by default.

API objects

The RBAC API declares four kinds of Kubernetes object: Role, ClusterRole, RoleBinding and ClusterRoleBinding. You can describe objects, or amend them, using tools such as kubectl, just like any other Kubernetes object.

Please check https://kubernetes.io/docs/reference/access-authn-authz/rbac/#api-overview for a comprenhensive description on how it works.

ClusterRole

An RBAC ClusterRole contains rules that represent a set of permissions. Permissions are purely additive (there are no “deny” rules).

StackGres handles different namespaces, so for the moment a ClusterRole is required to properly work.

ClusterRole example

The following example shows a ClusterRole with basic permisions for read stackgres resources:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: stackgres-reader
rules:
- apiGroups: [""]
  resources:
    - namespaces
    - pods
    - secrets
  verbs: ["get", "list"]
- apiGroups: ["storage.k8s.io"]
  resources:
    - storageclasses
  verbs: ["get", "list"]
- apiGroups: ["apiextensions.k8s.io"]
  resources:
    - customresourcedefinitions
  verbs: ["get", "list"]
- apiGroups: ["stackgres.io"]
  resources:
    - sgclusters
    - sgpgconfigs
    - sgbackupconfigs
    - sgbackups
    - sgdistributedlogs
    - sginstanceprofiles
    - sgpoolconfigs
  verbs: ["get", "list"]

ClusterRoleBinding

A role binding grants the permissions defined in a role to a user or set of users.

The following example “binds” the previous stackgres-reader ClusterRole to the example user:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  creationTimestamp: "2020-07-15T16:36:22Z"
  name: sg-restapi-example-user
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: stackgres-reader
subjects:
- apiGroup: rbac.authorization.k8s.io
  kind: User
  name: example

The same can be archived with: kubectl create clusterrolebinding sg-restapi-example-user --clusterrole=stackgres-reader --user=example

Please note that the example user must also be mapped in the secret with a password to be able to login to the Web UI.

Determine the Request Verb

The following is a table with the resources of StackGres that can be used for defining the ClusterRole:

Resource API Group Verbs
sgclusters stackgres.io get, list, create, update, patch, delete
sgpgconfigs stackgres.io get, list, create, update, patch, delete
sginstanceprofiles stackgres.io get, list, create, update, patch, delete
sgbackups stackgres.io get, list, create, update, patch, delete
sgbackupconfigs stackgres.io get, list, create, update, patch, delete
sgdistributedlogs stackgres.io get, list, create, update, patch, delete
sgpoolconfigs stackgres.io get, list, create, update, patch, delete
customresourcedefinitions apiextensions.k8s.io get, list
namespaces get, list
pods get, list
secrets get, list
storageclasses storage.k8s.io get, list

This is not an exhaustive list, but it should help to get started.