Overview

The authentication layer identifies the user associated with requests to the OpenShift Enterprise API. The authorization layer then uses information about the requesting user to determine if the request should be allowed.

As an administrator, you can configure authentication using a master configuration file.

Users and Groups

A user in OpenShift Enterprise is an entity that can make requests to the OpenShift Enterprise API. Typically, this represents the account of a developer or administrator that is interacting with OpenShift Enterprise.

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 OpenShift. These can be seen when viewing cluster bindings.

In the default set of virtual groups, note the following in particular:

Virtual Group Description

system:authenticated

Automatically associated with any currently-authenticated users.

system:unauthenticated

Automatically associated with any currently-unauthenticated users.

API Authentication

Requests to the OpenShift Enterprise API are authenticated using the following methods:

OAuth Access Tokens
  • Obtained from the OpenShift Enterprise OAuth server using the <master>/oauth/authorize and <master>/oauth/token endpoints.

  • Sent as an Authorization: Bearer…​ header or an access_token=…​ query parameter

X.509 Client Certificates
  • Requires a 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.

See the REST API Overview for more information and examples.

Impersonation

A request to the OpenShift Enterprise API may include an Impersonate-User header, which indicates that the requester wants to have the request handled as though it came from the specified user. This can be done on the command line by passing the --as=username flag.

Before User A is allowed to impersonate User B, User A is first authenticated. Then, an authorization check occurs to ensure that User A is allowed to impersonate the user named User B. If User A is requesting to impersonate a service account (system:serviceaccount:namespace:name), OpenShift Enterprise checks to ensure that User A can impersonate the serviceaccount named name in namespace. If the check fails, the request fails with a 403 (Forbidden) error code.

By default, project administrators and editors are allowed to impersonate service accounts in their namespace. The sudoers role allows a user to impersonate system:admin, which in turn has cluster administrator permissions. This grants some protection against typos (but not security) for someone administering the cluster. For example, oc delete nodes --all would be forbidden, but oc delete nodes --all --as=system:admin would be allowed. You can add a user to that group using oadm policy add-cluster-role-to-user sudoer <username>.

OAuth

The OpenShift Enterprise 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 Clients

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 OpenShift Enterprise API:

OAuth Client Usage

openshift-web-console

Requests tokens for the web console.

openshift-browser-client

Requests tokens at <master>/oauth/token/request with a user-agent that can handle interactive logins.

openshift-challenging-client

Requests tokens with a user-agent that can handle WWW-Authenticate challenges.

To register additional clients:

$ oc create -f <(echo '
{
  "kind": "OAuthClient",
  "apiVersion": "v1",
  "metadata": {
    "name": "demo" (1)
  },
  "secret": "...", (2)
  "redirectURIs": [
    "http://www.example.com/" (3)
  ]
}')
1 The name of the OAuth client is used as the client_id parameter when making requests to <master>/oauth/authorize and <master>/oauth/token.
2 The secret is used as the client_secret parameter when making requests to <master>/oauth/token.
3 The redirect_uri parameter specified in requests to <master>/oauth/authorize and <master>/oauth/token must be equal to (or prefixed by) one of the URIs in redirectURIs.

Integrations

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

If an authenticating proxy is placed in front of the <master>/oauth/authorize endpoint, it should send 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, Basic authentication challenges should only be sent if a X-CSRF-Token header is present on the request. Clients that expect to receive Basic WWW-Authenticate challenges should set this header to a non-empty value.

If the authenticating proxy cannot support WWW-Authenticate challenges, or if OpenShift Enterprise is configured to use an identity provider that does not support WWW-Authenticate challenges, users can visit <master>/oauth/token/request using a browser to obtain an access token manually.

Obtaining OAuth Tokens

The OAuth server supports standard authorization code grant and the implicit grant OAuth authorization flows.

When requesting an OAuth token using the implicit grant flow (response_type=token) with a client_id configured to request WWW-Authenticate challenges (like openshift-challenging-client), these are the possible server responses from /oauth/authorize, and how they should be handled:

Status Content Client response

302

Location header containing an access_token parameter in the URL fragment (RFC 4.2.2)

Use the access_token value as the OAuth token

302

Location header containing an error query parameter (RFC 4.1.2.1)

Fail, optionally surfacing the error (and optional error_description) query values to the user

302

Other Location header

Follow the redirect, and process the result using these rules

401

WWW-Authenticate header present

Respond to challenge if type is recognized (e.g. Basic, Negotiate, etc), resubmit request, and process the result using these rules

401

WWW-Authenticate header missing

No challenge authentication is possible. Fail and show response body (which might contain links or details on alternate methods to obtain an OAuth token)

Other

Other

Fail, optionally surfacing response body to the user