--- --- 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. ## ABAC Mode ### 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). - whether the request is for an API resource. - the request path. - allows authorizing access to miscellaneous endpoints like `/api` or `/healthz` (see [kubectl](#kubectl)). - the request verb. - API verbs like `get`, `list`, `create`, `update`, `watch`, `delete`, and `deletecollection` are used for API requests - HTTP verbs like `get`, `post`, `put`, and `delete` are used for non-API requests - what resource is being accessed (for API requests only) - the namespace of the object being accessed (for namespaced API requests only) - the API group being accessed (for API requests only) We anticipate adding more attributes to allow finer grained access control and to assist in policy management. ### 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. `*` matches all requests. - `group`, type string; if you specify `group`, it must match one of the groups of the authenticated user. `*` matches all requests. - `readonly`, type boolean, when true, means that the policy only applies to get, list, and watch operations. - Resource-matching properties: - `apiGroup`, type string; an API group, such as `extensions`. `*` matches all API groups. - `namespace`, type string; a namespace string. `*` matches all resource requests. - `resource`, type string; a resource, such as `pods`. `*` matches all resource requests. - Non-resource-matching properties: - `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. 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 user to do something, write a policy with the user property set to "*". 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: `{"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "alice", "namespace": "*", "resource": "*", "apiGroup": "*"}}` 2. Kubelet can read any pods: `{"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "kubelet", "namespace": "*", "resource": "pods", "readonly": true}}` 3. Kubelet can read and write events: `{"apiVersion": "abac.authorization.kubernetes.io/v1beta1", "kind": "Policy", "spec": {"user": "kubelet", "namespace": "*", "resource": "events"}}` 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}}` 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": "*"}}` [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.md/#Turn-on-or-off-an-api-version-for-your-cluster), with a `--runtime-config=` that includes `rbac.authorization.k8s.io/v1alpha1`. ### 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 default API Group. resources: ["pods"] verbs: ["get", "watch", "list"] nonResourceURLs: [] ``` `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 namespace: default name: pod-reader apiVersion: rbac.authorization.k8s.io/v1alpha1 ``` `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 apiVersion: rbac.authorization.k8s.io/v1alpha1 ``` 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 namepsace. ```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 subjects: - kind: Group # May be "User", "Group" or "ServiceAccount" name: manager roleRef: kind: ClusterRole name: secret-reader apiVersion: 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. For bootstrapping the first roles, it becomes necessary for someone to get around these limitations. For the alpha release of RBAC, an API Server flag was added to allow one user to step around all RBAC authorization and privilege escalation checks. NOTE: _This is subject to change with future releases._ ``` --authorization-rbac-super-user=admin ``` Once set the specified super user, in this case "admin", can be used to create the roles and role bindings to initialize the system. This flag is optional and once the initial bootstrapping is performed can be unset. ## 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 loser 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": "*", "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/*`, `/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.