Authorization

Within workspaces, KCP implements the same RBAC-based authorization mechanism as Kubernetes. Other authorization schemes (i.e. ABAC) are not supported. Generally, the same (cluster) role and (cluster) role binding principles apply exactly as in Kubernetes.

In addition, additional RBAC semantics is implemented cross-workspaces, namely the following:

Top-Level Organization access: the user must have this as pre-requisite to access any other workspace, or is even member and by that can create workspaces inside the organization workspace.
Workspace Content access: the user needs access to a workspace or is even admin.
for some resources, additional permission checks are performed, not represented by local or Kubernetes standard RBAC rules. E.g.
workspace creation checks for organization membership (see above).
workspace creation checks for use verb on the ClusterWorkspaceType.
API binding via APIBinding objects requires verb bind access to the corresponding APIExport.
System Workspaces access: system workspaces are prefixed with system: and are not accessible by users.

The details are outlined below.

Authorizers

The following authorizers are configured in kcp:

Authorizer	Description
Top-Level organization authorizer	checks that the user is allowed to access the organization
Workspace content authorizer	determines additional groups a user gets inside of a workspace
Maximal permission policy authorizer	validates the maximal permission policy RBAC policy in the API exporter workspace
Local Policy authorizer	validates the RBAC policy in the workspace that is accessed
Kubernetes Bootstrap Policy authorizer	validates the RBAC Kubernetes standard policy

They are related in the following way:

top-level organization authorizer must allow
workspace content authorizer must allow, and adds additional (virtual per-request) groups to the request user influencing the follow authorizers.
maximal permission policy authorizer must allow
one of the local authorizer or bootstrap policy authorizer must allow.

                                                                                          ┌──────────────┐
                                                                                          │              │
           ┌─────────────────┐     ┌───────────────┐        ┌───────────────────┐   ┌────►│ Local Policy ├──┐
           │ Top-level       │     │               │        │                   │   │     │ authorizer   │  │
 request   │ Organization    │     │ Workspace ┌───┴───┐    │ Max. Permission   │   │     │              │  │
──────────►│ authorizer      ├────►│ Content   │+groups├───►│ Policy authorizer ├───┤     └──────────────┘  │
           │                 │     │ authorizer└───┬───┘    │                   │   │                       ▼
           │                 │     │               │        └───────────────────┘   │                       OR───►
           └─────────────────┘     └───────────────┘                                │     ┌──────────────┐  ▲
                                                                                    │     │  Bootstrap   │  │
                                                                                    └────►│  Policy      ├──┘
                                                                                          │  authorizer  │
                                                                                          │              │
                                                                                          └──────────────┘

ASCIIFlow document)

Top-Level Organization authorizer

A top-level organization is a workspace directly under root. When a user accesses a top-level organization or a sub-workspace like root:org:ws:ws, this authorizer will check in root whether the user has permission to the top-level org workspace represented by the ClusterWorkspace named org in root with the following verbs:

Verb	Resource	Semantics
`access`	`clusterworkspace/content`	the user can access the organization `root:org`

E.g. the user is bound via a ClusterRoleBinding in root to a ClusterRole of the following shape:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  clusterName: root
rules:
- apiGroups:
  - tenancy.kcp.dev
  resources:
  - workspaces/content
  resourceNames:
  - org
  verbs:
  - access

Workspace Content authorizer

The workspace content authorizer checks whether the user is granted admin or access verbs in the parent workspace against the workspaces/content resource with the resourceNames of the workspace being accessed.

If any of the verbs is granted, the associated group is added to the user's attributes and will be evaluated in the subsequent authorizer chain.

Verb	Groups	Bootstrap cluster rolebinding
`admin`	`system:kcp:workspace:admin` and `system:kcp:workspace:access`	`system:kcp:clusterworkspace:admin`
`access`	`system:kcp:workspace:access`	N/A

kcp's bootstrap policy provides default bindings:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  clusterName: system:kcp:clusterworkspace:admin
subjects:
- kind: Group
  name: system:kcp:clusterworkspace:admin
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cluster-admin

The access verb will not grant any cluster role but only associates with the system:kcp:clusterworkspace:access group and executes the subsequent authorizer chain.

Example:

Given the user accesses root:org:ws:ws, the verbs admin and access are asserted against the workspaces/content resource for the resourceNames: ["ws"] in the workspace root:org:ws.

To give a user called "adam" admin access to a workspace root:org:ws:ws, beyond having org access using the previous top-level organization authorizer, a ClusterRole must be created in root:org:ws with the following shape:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: workspace-admin
  clusterName: root:org:ws
rules:
- apiGroups:
  - tenancy.kcp.dev
  resources:
  - workspaces/content
  resourceNames:
  - ws
  verbs:
  - admin

and the user must be bound to it via a ClusterRoleBinding in root:org:ws like the following:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: adam-admin
  clusterName: root:org:ws
subjects:
- kind: User
  name: adam
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: workspace-admin

Initializing Workspaces

By default, workspaces are only accessible to a user if they are in Ready phase. Workspaces that are initializing can be access only by users that are granted admin verb on the workspaces/content resource in the parent workspace.

Service accounts declared within a workspace don't have access to initializing workspaces.

Maximal permission policy authorizer

If the requested resource type is part of an API binding, then this authorizer verifies that the request is not exceeding the maximum permission policy of the related API export. Currently, the "local policy" maximum permission policy type is supported.

Local policy

The local maximum permission policy delegates the decision to the RBAC of the related API export. To distinguish between local RBAC role bindings in that workspace and those for this these maximum permission policy, every name and group is prefixed with apis.kcp.dev:binding:.

Example:

Given an API binding for type foo declared in workspace consumer that refers to an API export declared in workspace provider and a user user-1 having the group group-1 requesting a create of foo in the default namespace in the consumer workspace, this authorizer verifies that user-1 is allowed to execute this request by delegating to provider's RBAC using prefixed attributes.

Here, this authorizer prepends the apis.kcp.dev:binding: prefix to the username and all groups the user belongs to. Using prefixed attributes prevents RBAC collisions i.e. if user-1 is granted to execute requests within the provider workspace directly.

For the given example RBAC request looks as follows:

Username: apis.kcp.dev:binding:user-1
Group: apis.kcp.dev:binding:group-1
Resource: foo
Namespace: default
Workspace: provider
Verb: create

The following role and role binding declared within the provider workspace will grant access to the request:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: foo-creator
  clusterName: provider
rules:
- apiGroups:
  - foo.api
  resources:
  - foos
  verbs:
  - create
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: user-1-foo-creator
  namespace: default
  clusterName: provider
subjects:
- kind: User
  name: apis.kcp.dev:binding:user-1
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: foo-creator

Note

The same authorization scheme is enforced when executing the request of a claimed resource via the virtual API Export API server, i.e. a claimed resource is bound to the same maximal permission policy. Only the actual owner of that resources can go beyond that policy.

TBD: Example

Kubernetes Bootstrap Policy authorizer

The bootstrap policy authorizer works just like the local authorizer but references RBAC rules defined in the system:admin system workspace.

Local Policy authorizer

Once the top-level organization authorizer and the workspace content authorizer granted access to a workspace, RBAC rules contained in the workspace derived from the request context are evaluated.

This authorizer ensures that RBAC rules contained within a workspace are being applied and work just like in a regular Kubernetes cluster.

Note

Groups added by the workspace content authorizer can be used for role bindings in that workspace.

It is possible to bind to roles and cluster roles in the bootstrap policy from a local policy RoleBinding or ClusterRoleBinding.

Service Accounts

Kubernetes service accounts are granted access to the workspaces they are defined in and that are ready.

E.g. a service account "default" in root:org:ws:ws is granted access to root:org:ws:ws, and through the workspace content authorizer it gains the system:kcp:clusterworkspace:access group membership.