--- assignees: - erictune - lavalamp - deads2k - liggitt title: Using Authorization Plugins --- 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 policy. - `--authorization-mode=RBAC` is an experimental implementation which allows for authorization to be driven by the Kubernetes API. RBAC stands for Roles-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:: ``` Creating a new namespace also causes a new service account to be created, of this form: ```shell system:serviceaccount::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 1.3 RBAC mode is in alpha and considered experimental. To use RBAC, you must both enable the authorization module with `--authorization-mode=RBAC`, and [enable the API version]( /docs/admin/cluster-management/#turn-on-or-off-an-api-version-for-your-cluster), with a `--runtime-config=` that includes `rbac.authorization.k8s.io/v1alpha1`. ### Privilege Escalation Prevention and Bootstrapping The `rbac.authorization.k8s.io` API group inherently attempts to prevent users from escalating privileges. Simply put, __a user can't grant permissions they don't already have even when the RBAC authorizer it disabled__. If "user-1" does not have the ability to read secrets in "namespace-a", they cannot create a binding that would grant that permission to themselves or any other user. When bootstrapping, superuser credentials should include the `system:masters` group, for example by creating a client cert with `/O=system:masters`. This gives those credentials full access to the API and allows an admin to then set up bindings for other users. In Kubernetes versions 1.4 and 1.5, there was a similar flag that gave a user full access: ``` --authorization-rbac-super-user=admin ``` __This flag will be removed in 1.6__. Admins should prefer the `system:masters` group when setting up clusters. ### Roles, RolesBindings, ClusterRoles, and ClusterRoleBindings The RBAC API Group declares four top level types which will be covered in this section. Users can interact with these resources as they would with any other API resource. Through `kubectl`, direct calls to the API, etc. For instance, `kubectl create -f (resource).yml` can be used with any of these examples, though readers who wish to follow along should review the following section on bootstrapping first. In the RBAC API Group, roles hold a logical grouping of permissions. These permissions map very closely to ABAC policies, but only contain information about requests being made. Permission are purely additive, rules may only omit permissions they do not wish to grant. Here's an example of a role which grants read access to pods within the "default" namespace. ```yaml kind: Role apiVersion: rbac.authorization.k8s.io/v1alpha1 metadata: namespace: default name: pod-reader rules: - apiGroups: [""] # The API group "" indicates the core API Group. resources: ["pods"] verbs: ["get", "watch", "list"] ``` `ClusterRoles` hold the same information as a `Role` but can apply to any namespace as well as non-namespaced resources (such as `Nodes`, `PersistentVolume`, etc.). The following `ClusterRole` can grant permissions to read secrets in any namespace. ```yaml kind: ClusterRole apiVersion: rbac.authorization.k8s.io/v1alpha1 metadata: # "namespace" omitted since ClusterRoles are not namespaced. name: secret-reader rules: - apiGroups: [""] resources: ["secrets"] verbs: ["get", "watch", "list"] nonResourceURLs: [] ``` `RoleBindings` perform the task of granting the permission to a user or set of users. They hold a list of subjects which they apply to, and a reference to the `Role` being assigned. The following `RoleBinding` assigns the "pod-reader" role to the user "jane" within the "default" namespace, and allows jane to read pods. ```yaml # This role binding allows "jane" to read pods in the namespace "default" kind: RoleBinding apiVersion: rbac.authorization.k8s.io/v1alpha1 metadata: name: read-pods namespace: default subjects: - kind: User # May be "User", "Group" or "ServiceAccount" name: jane roleRef: kind: Role name: pod-reader apiGroup: rbac.authorization.k8s.io ``` `RoleBindings` may also refer to a `ClusterRole`. However, a `RoleBinding` that refers to a `ClusterRole` only applies in the `RoleBinding`'s namespace, not at the cluster level. This allows admins to define a set of common roles for the entire cluster, then reuse them in multiple namespaces. For instance, even though the following `RoleBinding` refers to a `ClusterRole`, "dave" (the subject) will only be able read secrets in the "development" namespace, the namespace of the `RoleBinding`. ```yaml # This role binding allows "dave" to read secrets in the namespace "development" kind: RoleBinding apiVersion: rbac.authorization.k8s.io/v1alpha1 metadata: name: read-secrets namespace: development # This binding only applies in the "development" namespace subjects: - kind: User # May be "User", "Group" or "ServiceAccount" name: dave roleRef: kind: ClusterRole name: secret-reader apiGroup: rbac.authorization.k8s.io ``` Finally a `ClusterRoleBinding` may be used to grant permissions in all namespaces. The following `ClusterRoleBinding` allows any user in the group "manager" to read secrets in any namespace. ```yaml # This cluster role binding allows anyone in the "manager" group to read secrets in any namespace. kind: ClusterRoleBinding apiVersion: rbac.authorization.k8s.io/v1alpha1 metadata: name: read-secrets-global subjects: - kind: Group # May be "User", "Group" or "ServiceAccount" name: manager roleRef: kind: ClusterRole  name: secret-reader apiGroup: rbac.authorization.k8s.io ``` ### Referring to Resources Most resources are represented by a string representation of their name, such as "pods", just as it appears in the URL for the relevant API endpoint. However, some Kubernetes APIs involve a "subresource" such as the logs for a pod. The URL for the pods logs endpoint is: ``` GET /api/v1/namespaces/{namespace}/pods/{name}/log ``` In this case, "pods" is the namespaced resource, and "log" is a subresource of pods. To represent this in an RBAC role, use a slash to delimit the resource and subresource names. To allow a subject to read both pods and pod logs, you would write: ```yaml kind: Role apiVersion: rbac.authorization.k8s.io/v1alpha1 metadata: namespace: default name: pod-and-pod-logs-reader rules: - apiGroups: [""] resources: ["pods", "pods/log"] verbs: ["get", "list"] ``` ### Referring to Subjects RoleBindings and ClusterRoleBindings bind "subjects" to "roles". Subjects can be groups, users or service accounts. Users are represented by strings. These can be plain usernames, like "alice", or email style names, like "bob@example.com", or numeric ids as string. It is up to the Kubernetes admin to configure the [authentication modules](/docs/admin/authentication/) to produce usernames in the desired format. The RBAC authorization system does not require any particular format. However, the prefix `system:` is reserved for Kubernetes system use, and so the admin should ensure usernames should not contain this prefix by accident. Groups information in Kubernetes is currently provided by the Authenticator modules. (In the future we may add a separate way for the RBAC Authorizer to query groups information for users.) Groups, like users, are represented by a string, and that string has no format requirements, other than that the prefix `system:` is reserved. Service Accounts have usernames with the `system:` prefix and belong to groups with the `system:` prefix. #### Role Binding Examples Only the `subjects` section of a RoleBinding object shown in the following examples. For a user called `alice@example.com`, specify ```yaml subjects: - kind: User name: "alice@example.com" ``` For a group called `frontend-admins`, specify: ```yaml subjects: - kind: Group name: "frontend-admins" ``` For the default service account in the kube-system namespace: ```yaml subjects: - kind: ServiceAccount name: default namespace: kube-system ``` For all service accounts in the `qa` namespace: ```yaml subjects: - kind: Group name: system:serviceaccounts:qa ``` For all service accounts everywhere: ```yaml subjects: - kind: Group name: system:serviceaccounts ``` For all authenticated users: ```yaml subjects: - kind: Group name: system:authenticated ``` For all unauthenticated users: ```yaml subjects: - kind: Group name: system:unauthenticated ``` For all users: ```yaml subjects: - kind: Group name: system:authenticated - kind: Group name: system:unauthenticated ``` ## 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/concepts/cluster-administration/authenticate-across-clusters-kubeconfig/) 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.