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196 lines
9.2 KiB
Markdown
196 lines
9.2 KiB
Markdown
<!-- BEGIN MUNGE: UNVERSIONED_WARNING -->
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<!-- BEGIN STRIP_FOR_RELEASE -->
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>
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If you are using a released version of Kubernetes, you should
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refer to the docs that go with that version.
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<!-- TAG RELEASE_LINK, added by the munger automatically -->
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<strong>
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The latest release of this document can be found
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[here](http://releases.k8s.io/release-1.1/docs/admin/authorization.md).
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Documentation for other releases can be found at
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[releases.k8s.io](http://releases.k8s.io).
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</strong>
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--
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<!-- END STRIP_FOR_RELEASE -->
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<!-- END MUNGE: UNVERSIONED_WARNING -->
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# Authorization Plugins
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In Kubernetes, authorization happens as a separate step from authentication.
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See the [authentication documentation](authentication.md) for an
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overview of authentication.
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Authorization applies to all HTTP accesses on the main (secure) apiserver port.
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The authorization check for any request compares attributes of the context of
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the request, (such as user, resource, and namespace) with access
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policies. An API call must be allowed by some policy in order to proceed.
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The following implementations are available, and are selected by flag:
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- `--authorization-mode=AlwaysDeny`
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- `--authorization-mode=AlwaysAllow`
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- `--authorization-mode=ABAC`
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`AlwaysDeny` blocks all requests (used in tests).
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`AlwaysAllow` allows all requests; use if you don't need authorization.
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`ABAC` allows for user-configured authorization policy. ABAC stands for Attribute-Based Access Control.
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## ABAC Mode
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### Request Attributes
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A request has the following attributes that can be considered for authorization:
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- user (the user-string which a user was authenticated as).
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- group (the list of group names the authenticated user is a member of).
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- whether the request is for an API resource.
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- the request path.
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- allows authorizing access to miscellaneous endpoints like `/api` or `/healthz` (see [kubectl](#kubectl)).
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- the request verb.
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- API verbs like `get`, `list`, `create`, `update`, `watch`, `delete`, and `deletecollection` are used for API requests
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- HTTP verbs like `get`, `post`, `put`, and `delete` are used for non-API requests
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- what resource is being accessed (for API requests only)
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- the namespace of the object being accessed (for namespaced API requests only)
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- the API group being accessed (for API requests only)
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We anticipate adding more attributes to allow finer grained access control and
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to assist in policy management.
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### Policy File Format
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For mode `ABAC`, also specify `--authorization-policy-file=SOME_FILENAME`.
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The file format is [one JSON object per line](http://jsonlines.org/). There should be no enclosing list or map, just
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one map per line.
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Each line is a "policy object". A policy object is a map with the following properties:
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- Versioning properties:
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- `apiVersion`, type string; valid values are "abac.authorization.kubernetes.io/v1beta1". Allows versioning and conversion of the policy format.
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- `kind`, type string: valid values are "Policy". Allows versioning and conversion of the policy format.
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- `spec` property set to a map with the following properties:
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- Subject-matching properties:
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- `user`, type string; the user-string from `--token-auth-file`. If you specify `user`, it must match the username of the authenticated user. `*` matches all requests.
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- `group`, type string; if you specify `group`, it must match one of the groups of the authenticated user. `*` matches all requests.
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- `readonly`, type boolean, when true, means that the policy only applies to get, list, and watch operations.
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- Resource-matching properties:
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- `apiGroup`, type string; an API group, such as `extensions`. `*` matches all API groups.
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- `namespace`, type string; a namespace string. `*` matches all resource requests.
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- `resource`, type string; a resource, such as `pods`. `*` matches all resource requests.
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- Non-resource-matching properties:
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- `nonResourcePath`, type string; matches the non-resource request paths (like `/version` and `/apis`). `*` matches all non-resource requests. `/foo/*` matches `/foo/` and all of its subpaths.
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An unset property is the same as a property set to the zero value for its type (e.g. empty string, 0, false).
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However, unset should be preferred for readability.
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In the future, policies may be expressed in a JSON format, and managed via a REST interface.
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### Authorization Algorithm
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A request has attributes which correspond to the properties of a policy object.
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When a request is received, the attributes are determined. Unknown attributes
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are set to the zero value of its type (e.g. empty string, 0, false).
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A property set to "*" will match any value of the corresponding attribute.
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The tuple of attributes is checked for a match against every policy in the policy file.
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If at least one line matches the request attributes, then the request is authorized (but may fail later validation).
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To permit any user to do something, write a policy with the user property set to "*".
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To permit a user to do anything, write a policy with the apiGroup, namespace, resource, and nonResourcePath properties set to "*".
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### Kubectl
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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`.
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When using ABAC authorization, those special resources have to be explicitly exposed via the `nonResourcePath` property in a policy (see [examples](#examples) below):
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* `/api`, `/api/*`, `/apis`, and `/apis/*` for API version negotiation.
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* `/version` for retrieving the server version via `kubectl version`.
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* `/swaggerapi/*` for create/update operations.
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To inspect the HTTP calls involved in a specific kubectl operation you can turn up the verbosity:
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kubectl --v=8 version
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### Examples
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1. Alice can do anything to all resources: `{"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "alice", "namespace": "*", "resource": "*", "apiGroup": "*"}}`
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2. Kubelet can read any pods: `{"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "kubelet", "namespace": "*", "resource": "pods", "readonly": true}}`
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3. Kubelet can read and write events: `{"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "kubelet", "namespace": "*", "resource": "events"}}`
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4. Bob can just read pods in namespace "projectCaribou": `{"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "bob", "namespace": "projectCaribou", "resource": "pods", "readonly": true}}`
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5. Anyone can make read-only requests to all non-API paths: `{"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "*", "readonly": true, "nonResourcePath": "*"}}`
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[Complete file example](http://releases.k8s.io/HEAD/pkg/auth/authorizer/abac/example_policy_file.jsonl)
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### A quick note on service accounts
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A service account automatically generates a user. The user's name is generated according to the naming convention:
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```
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system:serviceaccount:<namespace>:<serviceaccountname>
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```
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Creating a new namespace also causes a new service account to be created, of this form:*
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```
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system:serviceaccount:<namespace>:default
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```
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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:
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```json
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{"apiVersion":"abac.authorization.kubernetes.io/v1beta1","kind":"Policy","user":"system:serviceaccount:kube-system:default","namespace":"*","resource":"*","apiGroup":"*"}
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```
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The apiserver will need to be restarted to pickup the new policy lines.
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## Plugin Development
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Other implementations can be developed fairly easily.
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The APIserver calls the Authorizer interface:
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```go
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type Authorizer interface {
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Authorize(a Attributes) error
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}
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```
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to determine whether or not to allow each API action.
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An authorization plugin is a module that implements this interface.
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Authorization plugin code goes in `pkg/auth/authorizer/$MODULENAME`.
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An authorization module can be completely implemented in go, or can call out
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to a remote authorization service. Authorization modules can implement
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their own caching to reduce the cost of repeated authorization calls with the
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same or similar arguments. Developers should then consider the interaction between
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caching and revocation of permissions.
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<!-- BEGIN MUNGE: GENERATED_ANALYTICS -->
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[]()
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<!-- END MUNGE: GENERATED_ANALYTICS -->
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