website/docs/admin/authorization/index.md

---
assignees:
- erictune
- lavalamp
- deads2k
- liggitt
title: Overview
---

In Kubernetes, authorization happens as a separate step from authentication.
See the [Accessing Control Overview](/docs/admin/accessing-the-api/) for an
overview of how authentication and authorization are applied to requests.

Authorization applies to all HTTP accesses on the main (secure) apiserver port.

The authorization check for any request compares attributes of the context of
the request, (such as user, resource, and namespace) with access
policies.  An API call must be allowed by some policy in order to proceed.

The following implementations are available, and are selected by flag:

  - `--authorization-mode=AlwaysDeny` blocks all requests (used in tests).
  - `--authorization-mode=AlwaysAllow` allows all requests; use if you don't
need authorization.
  - `--authorization-mode=ABAC` allows for a simple local-file-based user-configured
authorization policy.  ABAC stands for Attribute-Based Access Control.
  - `--authorization-mode=RBAC` allows for authorization to be driven by policy
stored in the Kubernetes API. RBAC stands for Role-Based Access Control.
  - `--authorization-mode=Webhook` allows for authorization to be driven by a
remote service using REST.

If multiple modes are provided the set is unioned, and only a single authorizer is required to admit the action.  This means the flag:

```
--authorization-mode=AlwaysDeny,AlwaysAllow
```

will always allow.

## Request Attributes

A request has the following attributes that can be considered for authorization:

  - user (the user-string which a user was authenticated as).
  - group (the list of group names the authenticated user is a member of).
  - "extra" (a map of arbitrary string keys to string values, provided by the authentication layer)
  - whether the request is for an API resource.
  - the request path.
    - allows authorizing access to miscellaneous non-resource endpoints like `/api` or `/healthz` (see [kubectl](#kubectl)).
  - the request verb.
    - API verbs `get`, `list`, `create`, `update`, `patch`, `watch`, `proxy`, `redirect`, `delete`, and `deletecollection` are used for resource requests
    - HTTP verbs `get`, `post`, `put`, and `delete` are used for non-resource requests
  - what resource is being accessed (for resource requests only)
  - what subresource is being accessed (for resource requests only)
  - the namespace of the object being accessed (for namespaced resource requests only)
  - the API group being accessed (for resource requests only); an empty string designates the [core API group](/docs/api/)

The request verb for a resource API endpoint can be determined by the HTTP verb used and whether or not the request acts on an individual resource or a collection of resources:

HTTP verb | request verb
----------|---------------
POST      | create
GET, HEAD | get (for individual resources), list (for collections)
PUT       | update
PATCH     | patch
DELETE    | delete (for individual resources), deletecollection (for collections)


## ABAC Mode

### Policy File Format

For mode `ABAC`, also specify `--authorization-policy-file=SOME_FILENAME`.

The file format is [one JSON object per line](http://jsonlines.org/).  There
should be no enclosing list or map, just one map per line.

Each line is a "policy object".  A policy object is a map with the following
properties:

  - Versioning properties:
    - `apiVersion`, type string; valid values are "abac.authorization.kubernetes.io/v1beta1". Allows versioning and conversion of the policy format.
    - `kind`, type string: valid values are "Policy". Allows versioning and conversion of the policy format.
  - `spec` property set to a map with the following properties:
    - Subject-matching properties:
      - `user`, type string; the user-string from `--token-auth-file`. If you specify `user`, it must match the username of the authenticated user.
      - `group`, type string; if you specify `group`, it must match one of the groups of the authenticated user. `system:authenticated` matches all authenticated requests. `system:unauthenticated` matches all unauthenticated requests.
    - Resource-matching properties:
      - `apiGroup`, type string; an API group.
        - Ex: `extensions`
        - Wildard: `*` matches all API groups.
      - `namespace`, type string; a namespace.
        - Ex: `kube-system`
        - Wildard: `*` matches all resource requests.
      - `resource`, type string; a resource type
        - Ex: `pods`
        - Wildcard: `*` matches all resource requests.
    - Non-resource-matching properties:
      - `nonResourcePath`, type string; non-resource request paths.
        - Ex: `/version` or `/apis`
        - Wildcard: 
          - `*` matches all non-resource requests.
          - `/foo/*` matches `/foo/` and all of its subpaths.
    - `readonly`, type boolean, when true, means that the policy only applies to get, list, and watch operations.

**NOTES:** An unset property is the same as a property set to the zero value for its type
(e.g. empty string, 0, false). However, unset should be preferred for
readability.

In the future, policies may be expressed in a JSON format, and managed via a
REST interface.

### Authorization Algorithm

A request has attributes which correspond to the properties of a policy object.

When a request is received, the attributes are determined.  Unknown attributes
are set to the zero value of its type (e.g. empty string, 0, false).

A property set to `"*"` will match any value of the corresponding attribute.

The tuple of attributes is checked for a match against every policy in the
policy file. If at least one line matches the request attributes, then the
request is authorized (but may fail later validation).

To permit any authenticated user to do something, write a policy with the
group property set to `"system:authenticated"`.

To permit any unauthenticated user to do something, write a policy with the
group property set to `"system:unauthenticated"`.

To permit a user to do anything, write a policy with the apiGroup, namespace,
resource, and nonResourcePath properties set to `"*"`.

### Kubectl

Kubectl uses the `/api` and `/apis` endpoints of api-server to negotiate
client/server versions. To validate objects sent to the API by create/update
operations, kubectl queries certain swagger resources. For API version `v1`
those would be `/swaggerapi/api/v1` & `/swaggerapi/experimental/v1`.

When using ABAC authorization, those special resources have to be explicitly
exposed via the `nonResourcePath` property in a policy (see [examples](#examples) below):

* `/api`, `/api/*`, `/apis`, and `/apis/*` for API version negotiation.
* `/version` for retrieving the server version via `kubectl version`.
* `/swaggerapi/*` for create/update operations.

To inspect the HTTP calls involved in a specific kubectl operation you can turn
up the verbosity:

    kubectl --v=8 version

### Examples

 1. Alice can do anything to all resources:

    ```json
    {"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "alice", "namespace": "*", "resource": "*", "apiGroup": "*"}}
    ```
 2. Kubelet can read any pods:

    ```json
    {"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "kubelet", "namespace": "*", "resource": "pods", "readonly": true}}
    ```
 3. Kubelet can read and write events:

    ```json
    {"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "kubelet", "namespace": "*", "resource": "events"}}
    ```
 4. Bob can just read pods in namespace "projectCaribou":

    ```json
    {"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "bob", "namespace": "projectCaribou", "resource": "pods", "readonly": true}}
    ```
 5. Anyone can make read-only requests to all non-resource paths:

    ```json
    {"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"group": "system:authenticated", "readonly": true, "nonResourcePath": "*"}}
    {"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"group": "system:unauthenticated", "readonly": true, "nonResourcePath": "*"}}
    ```

[Complete file example](http://releases.k8s.io/{{page.githubbranch}}/pkg/auth/authorizer/abac/example_policy_file.jsonl)

### A quick note on service accounts

A service account automatically generates a user. The user's name is generated
according to the naming convention:

```shell
system:serviceaccount:<namespace>:<serviceaccountname>
```
Creating a new namespace also causes a new service account to be created, of
this form:

```shell
system:serviceaccount:<namespace>:default
```

For example, if you wanted to grant the default service account in the
kube-system full privilege to the API, you would add this line to your policy
file:

```json
{"apiVersion":"abac.authorization.kubernetes.io/v1beta1","kind":"Policy","spec":{"user":"system:serviceaccount:kube-system:default","namespace":"*","resource":"*","apiGroup":"*"}}
```

The apiserver will need to be restarted to pickup the new policy lines.

## RBAC Mode

When specified "RBAC" (Role-Based Access Control) uses the
"rbac.authorization.k8s.io" API group to drive authorization decisions,
allowing admins to dynamically configure permission policies through the
Kubernetes API.

As of 1.6 RBAC mode is in beta.

To enable RBAC, start the apiserver with `--authorization-mode=RBAC`.

For details about administrating and using RBAC, view the [RBAC guide](/docs/admin/authorization/rbac).

## Webhook Mode

When specified, mode `Webhook` causes Kubernetes to query an outside REST
service when determining user privileges.

### Configuration File Format

Mode `Webhook` requires a file for HTTP configuration, specify by the
`--authorization-webhook-config-file=SOME_FILENAME` flag.

The configuration file uses the [kubeconfig](/docs/user-guide/kubeconfig-file/)
file format. Within the file "users" refers to the API Server webhook and
"clusters" refers to the remote service.

A configuration example which uses HTTPS client auth:

```yaml
# clusters refers to the remote service.
clusters:
  - name: name-of-remote-authz-service
    cluster:
      certificate-authority: /path/to/ca.pem      # CA for verifying the remote service.
      server: https://authz.example.com/authorize # URL of remote service to query. Must use 'https'.

# users refers to the API Server's webhook configuration.
users:
  - name: name-of-api-server
    user:
      client-certificate: /path/to/cert.pem # cert for the webhook plugin to use
      client-key: /path/to/key.pem          # key matching the cert

# kubeconfig files require a context. Provide one for the API Server.
current-context: webhook
contexts:
- context:
    cluster: name-of-remote-authz-service
    user: name-of-api-sever
  name: webhook
```

### Request Payloads

When faced with an authorization decision, the API Server POSTs a JSON
serialized api.authorization.v1beta1.SubjectAccessReview object describing the
action. This object contains fields describing the user attempting to make the
request, and either details about the resource being accessed or requests
attributes.

Note that webhook API objects are subject to the same [versioning compatibility rules](/docs/api/)
as other Kubernetes API objects. Implementers should be aware of looser
compatibility promises for beta objects and check the "apiVersion" field of the
request to ensure correct deserialization. Additionally, the API Server must
enable the `authorization.k8s.io/v1beta1` API extensions group (`--runtime-config=authorization.k8s.io/v1beta1=true`).

An example request body:

```json
{
  "apiVersion": "authorization.k8s.io/v1beta1",
  "kind": "SubjectAccessReview",
  "spec": {
    "resourceAttributes": {
      "namespace": "kittensandponies",
      "verb": "GET",
      "group": "unicorn.example.org",
      "resource": "pods"
    },
    "user": "jane",
    "group": [
      "group1",
      "group2"
    ]
  }
}
```

The remote service is expected to fill the SubjectAccessReviewStatus field of
the request and respond to either allow or disallow access. The response body's
"spec" field is ignored and may be omitted. A permissive response would return:

```json
{
  "apiVersion": "authorization.k8s.io/v1beta1",
  "kind": "SubjectAccessReview",
  "status": {
    "allowed": true
  }
}
```

To disallow access, the remote service would return:

```json
{
  "apiVersion": "authorization.k8s.io/v1beta1",
  "kind": "SubjectAccessReview",
  "status": {
    "allowed": false,
    "reason": "user does not have read access to the namespace"
  }
}
```

Access to non-resource paths are sent as:

```json
{
  "apiVersion": "authorization.k8s.io/v1beta1",
  "kind": "SubjectAccessReview",
  "spec": {
    "nonResourceAttributes": {
      "path": "/debug",
      "verb": "GET"
    },
    "user": "jane",
    "group": [
      "group1",
      "group2"
    ]
  }
}
```

Non-resource paths include: `/api`, `/apis`, `/metrics`, `/resetMetrics`,
`/logs`, `/debug`, `/healthz`, `/swagger-ui/`, `/swaggerapi/`, `/ui`, and
`/version.` Clients require access to `/api`, `/api/*`, `/apis`, `/apis/*`,
and `/version` to discover what resources and versions are present on the server.
Access to other non-resource paths can be disallowed without restricting access
to the REST api.

For further documentation refer to the authorization.v1beta1 API objects and
plugin/pkg/auth/authorizer/webhook/webhook.go.

## Module Development

Other implementations can be developed fairly easily.
The APIserver calls the Authorizer interface:

```go
type Authorizer interface {
  Authorize(a Attributes) error
}
```

to determine whether or not to allow each API action.

An authorization plugin is a module that implements this interface.
Authorization plugin code goes in `pkg/auth/authorizer/$MODULENAME`.

An authorization module can be completely implemented in go, or can call out
to a remote authorization service.  Authorization modules can implement
their own caching to reduce the cost of repeated authorization calls with the
same or similar arguments.  Developers should then consider the interaction
between caching and revocation of permissions.


### Checking API Access

Kubernetes exposes the `subjectaccessreviews.v1beta1.authorization.k8s.io` resource as a
normal resource that allows external access to API authorizer decisions.  No matter which authorizer
you choose to use, you can issue a `POST` with a `SubjectAccessReview` just like the webhook
authorizer to the `apis/authorization.k8s.io/v1beta1/subjectaccessreviews` endpoint and
get back a response.  For instance:

```bash
kubectl create --v=8 -f -  << __EOF__
{
  "apiVersion": "authorization.k8s.io/v1beta1",
  "kind": "SubjectAccessReview",
  "spec": {
    "resourceAttributes": {
      "namespace": "kittensandponies",
      "verb": "GET",
      "group": "unicorn.example.org",
      "resource": "pods"
    },
    "user": "jane",
    "group": [
      "group1",
      "group2"
    ]
  }
}
__EOF__

--- snip lots of output ---

I0913 08:12:31.362873   27425 request.go:908] Response Body: {"kind":"SubjectAccessReview","apiVersion":"authorization.k8s.io/v1beta1","metadata":{"creationTimestamp":null},"spec":{"resourceAttributes":{"namespace":"kittensandponies","verb":"GET","group":"unicorn.example.org","resource":"pods"},"user":"jane","group":["group1","group2"]},"status":{"allowed":true}}
subjectaccessreview "" created
```

This is useful for debugging access problems, in that you can use this resource
to determine what access an authorizer is granting.