Understanding authentication

Understanding authentication

For users to interact with OKD, they must first authenticate to the cluster. The authentication layer identifies the user associated with requests to the OKD API. The authorization layer then uses information about the requesting user to determine if the request is allowed.

As an administrator, you can configure authentication for OKD.

Users

A user in OKD is an entity that can make requests to the OKD API. An OKD User object represents an actor which can be granted permissions in the system by adding roles to them or to their groups. Typically, this represents the account of a developer or administrator that is interacting with OKD.

Several types of users can exist:

User type	Description
`Regular users`	This is the way most interactive OKD users are represented. Regular users are created automatically in the system upon first login or can be created via the API. Regular users are represented with the `User` object. Examples: `joe` `alice`
`System users`	Many of these are created automatically when the infrastructure is defined, mainly for the purpose of enabling the infrastructure to interact with the API securely. They include a cluster administrator (with access to everything), a per-node user, users for use by routers and registries, and various others. Finally, there is an `anonymous` system user that is used by default for unauthenticated requests. Examples: `system:admin` `system:openshift-registry` `system:node:node1.example.com`
`Service accounts`	These are special system users associated with projects; some are created automatically when the project is first created, while project administrators can create more for the purpose of defining access to the contents of each project. Service accounts are represented with the `ServiceAccount` object. Examples: `system:serviceaccount:default:deployer` `system:serviceaccount:foo:builder`

Each user must authenticate in some way to access OKD. API requests with no authentication or invalid authentication are authenticated as requests by the anonymous system user. After authentication, policy determines what the user is authorized to do.

Groups

A user can be assigned to one or more groups, each of which represent a certain set of users. Groups are useful when managing authorization policies to grant permissions to multiple users at once, for example allowing access to objects within a project, versus granting them to users individually.

In addition to explicitly defined groups, there are also system groups, or virtual groups, that are automatically provisioned by the cluster.

The following default virtual groups are most important:

Virtual group	Description
`system:authenticated`	Automatically associated with all authenticated users.
`system:authenticated:oauth`	Automatically associated with all users authenticated with an OAuth access token.
`system:unauthenticated`	Automatically associated with all unauthenticated users.

API authentication

Requests to the OKD API are authenticated using the following methods:

OAuth access tokens

Obtained from the OKD OAuth server using the _<namespace_route>_/oauth/authorize and _<namespace_route>_/oauth/token endpoints.
Sent as an Authorization: Bearer… header.
Sent as a websocket subprotocol header in the form base64url.bearer.authorization.k8s.io.<base64url-encoded-token> for websocket requests.

X.509 client certificates

Requires an HTTPS connection to the API server.
Verified by the API server against a trusted certificate authority bundle.
The API server creates and distributes certificates to controllers to authenticate themselves.

Any request with an invalid access token or an invalid certificate is rejected by the authentication layer with a 401 error.

If no access token or certificate is presented, the authentication layer assigns the system:anonymous virtual user and the system:unauthenticated virtual group to the request. This allows the authorization layer to determine which requests, if any, an anonymous user is allowed to make.

OKD OAuth server

The OKD master includes a built-in OAuth server. Users obtain OAuth access tokens to authenticate themselves to the API.

When a person requests a new OAuth token, the OAuth server uses the configured identity provider to determine the identity of the person making the request.

It then determines what user that identity maps to, creates an access token for that user, and returns the token for use.

OAuth token requests

Every request for an OAuth token must specify the OAuth client that will receive and use the token. The following OAuth clients are automatically created when starting the OKD API:

OAuth client	Usage
`openshift-browser-client`	Requests tokens at `<namespace_route>/oauth/token/request` with a user-agent that can handle interactive logins. ^[1]
`openshift-challenging-client`	Requests tokens with a user-agent that can handle `WWW-Authenticate` challenges.

<namespace_route> refers to the namespace route. This is found by running the following command:
```
$ oc get route oauth-openshift -n openshift-authentication -o json | jq .spec.host
```

All requests for OAuth tokens involve a request to <namespace_route>/oauth/authorize. Most authentication integrations place an authenticating proxy in front of this endpoint, or configure OKD to validate credentials against a backing identity provider. Requests to <namespace_route>/oauth/authorize can come from user-agents that cannot display interactive login pages, such as the CLI. Therefore, OKD supports authenticating using a WWW-Authenticate challenge in addition to interactive login flows.

If an authenticating proxy is placed in front of the <namespace_route>/oauth/authorize endpoint, it sends unauthenticated, non-browser user-agents WWW-Authenticate challenges rather than displaying an interactive login page or redirecting to an interactive login flow.

To prevent cross-site request forgery (CSRF) attacks against browser clients, only send Basic authentication challenges with if a X-CSRF-Token header is on the request. Clients that expect to receive Basic WWW-Authenticate challenges must set this header to a non-empty value.

If the authenticating proxy cannot support WWW-Authenticate challenges, or if OKD is configured to use an identity provider that does not support WWW-Authenticate challenges, you must use a browser to manually obtain a token from <namespace_route>/oauth/token/request.

API impersonation

You can configure a request to the OKD API to act as though it originated from another user. For more information, see User impersonation in the Kubernetes documentation.

Authentication metrics for Prometheus

OKD captures the following Prometheus system metrics during authentication attempts:

openshift_auth_basic_password_count counts the number of oc login user name and password attempts.
openshift_auth_basic_password_count_result counts the number of oc login user name and password attempts by result, success or error.
openshift_auth_form_password_count counts the number of web console login attempts.
openshift_auth_form_password_count_result counts the number of web console login attempts by result, success or error.
openshift_auth_password_total counts the total number of oc login and web console login attempts.