TokenX

Abstract

Abstract

What is TokenX?

TokenX is the short term for OAuth 2.0 Token Exchange implemented in the context of Kubernetes.

It consists of mainly 3 components:

• Tokendings - an OAuth 2.0 Authorization Server implementing the OAuth 2.0 Token Exchange specification
• Jwker - a Kubernetes operator responsible for registering applications as OAuth 2.0 clients in Tokendings
• Naiserator - a Kubernetes operator that handles the lifecycle of applications on the NAIS platform

In short, TokenX is a OAuth 2.0 compliant add-on that enables and allows your application to maintain the zero trust networking principles (together with components such as LinkerD). It does this by allowing applications to exchange and acquire properly scoped security tokens in order to securely communicate with each other.

Interested readers may find more technical details in the Tokendings documentation.

Why do I need TokenX?

In a zero trust architecture, one cannot rely on traditional boundaries such as security zones and security gateways. Such security measures are no longer required for applications that leverage TokenX correctly as each application is self-contained within its own zone; requiring specific tokens in order to communicate with other applications.

Using TokenX correctly throughout a call-chain also ensures that the identity of the original caller or subject (e.g. an end-user) is propagated while still maintaining proper scoping and security between each application.

When do I need TokenX?

There are primarily two distinct cases where one must use TokenX:

1. You have a user facing app using ID-porten that should perform calls to another app on behalf of a user.
2. You have an app receiving tokens issued from Tokendings and need to call another app while still propagating the original user context.

Overview of flow

Configuration

Spec

See the NAIS manifest.

Getting Started

nais.yaml

spec:
  tokenx:
    enabled: true
  accessPolicy:
    inbound:
      rules:
        - application: app-2
        - application: app-3
          namespace: team-a
        - application: app-4
          namespace: team-b
          cluster: prod-gcp

Access Policies

In order for other applications to acquire a token targeting your application, you must explicitly specify inbound access policies that authorizes these other applications.

Thus, the access policies defines authorization on the application layer, and is enforced by Tokendings on token exchange operations.

For example:

spec:
  tokenx:
    enabled: true
  accessPolicy:
    inbound:
      rules:
        - application: app-1
        - application: app-2
          namespace: team-a
        - application: app-3
          namespace: team-b
          cluster: prod-gcp

The above configuration authorizes the following applications:

• application app-1 running in the same namespace and same cluster as your application
• application app-2 running in the namespace team-a in the same cluster
• application app-3 running in the namespace team-b in the cluster prod-gcp

Usage

Runtime Variables & Credentials

Enabling TokenX will expose the following runtime environment variables and files (under the directory /var/run/secrets/nais.io/jwker) for your application:

---

TOKEN_X_WELL_KNOWN_URL

Note

The well-known URL for the OAuth 2.0 Token Exchange authorization server (in this case, Tokendings) metadata document.

Example value: https://tokendings.dev-gcp.nais.io/.well-known/oauth-authorization-server

---

TOKEN_X_CLIENT_ID

Note

Client ID that uniquely identifies the application in TokenX. It has the following naming scheme:

<cluster>:<metadata.namespace>:<metadata.name>

This value should be used in the client assertion when exchanging a token with Tokendings.

---

TOKEN_X_PRIVATE_JWK

Note

Private JWK containing an RSA key belonging to your client. Used to sign client assertions during client authentication.

{
    "use": "sig",
    "kty": "RSA",
    "kid": "jXDxKRE6a4jogcc4HgkDq3uVgQ0",
    "n": "xQ3chFsz...",
    "e": "AQAB",
    "d": "C0BVXQFQ...",
    "p": "9TGEF_Vk...",
    "q": "zb0yTkgqO...",
    "dp": "7YcKcCtJ...",
    "dq": "sXxLHp9A...",
    "qi": "QCW5VQjO..."
}

TOKEN_X_ISSUER

Note

issuer from the metadata discovery document.

Example value: https://tokendings.dev-gcp.nais.io

---

TOKEN_X_JWKS_URI

Note

jwks_uri from the metadata discovery document.

Example value: https://tokendings.dev-gcp.nais.io/jwks

---

TOKEN_X_TOKEN_ENDPOINT

Note

token_endpoint from the metadata discovery document.

Example value: https://tokendings.dev-gcp.nais.io/token

---

Client Authentication

Your application must authenticate itself with Tokendings when attempting to perform token exchanges. To do so, you must create a client assertion.

In other words, you must create a JWT that is signed by your application using the private key contained within TOKEN_X_PRIVATE_JWK.

The assertion must contain the following claims:

Claim	Example Value	Description
sub	dev-gcp:aura:app-a	The subject of the token. Must be set to your application's own client_id.
iss	dev-gcp:aura:app-a	The issuer of the token. Must be set to your application's own client_id.
aud	https://tokendings.dev-gcp.nais.io/token	The audience of the token. Must be set to the token_endpoint of Tokendings. The value of this exists in the metadata found at the well-known endpoint.
jti	83c580a6-b479-426d-876b-267aa9848e2f	The JWT ID of the token. Used to uniquely identify a token. Set this to a UUID or similar.
nbf	1597783152	nbf stands for not before. It identifies the time (seconds after Epoch) before which the JWT MUST NOT be accepted for processing.
iat	1597783152	iat stands for issued at. It identifies the time (seconds after Epoch) in which the JWT was issued (or created).
exp	1597783272	exp is the expiration time (seconds after Epoch) of the token. This must not be more than 120 seconds after nbf and iat. That is, the maximum lifetime of the token must be no greater than 120 seconds.

Additionally, the headers of the assertion must contain the following parameters:

Parameter	Value	Description
kid	93ad09a5-70bc-4858-bd26-5ff4a0c5f73f	The key identifier of the key used to sign the assertion. This identifier is available in the JWK found in TOKEN_X_PRIVATE_JWK.
typ	JWT	Represents the type of this JWT. Set this to JWT.
alg	RS256	Represents the cryptographic algorithm used to secure the JWT. Set this to RS256.

An assertion should be unique and not be reused when authenticating with Tokendings in accordance with the security considerations in RFC 7521.

That is, every request to Tokendings should contain a unique client assertion:

• Set the JWT ID (jti) claim to a unique value, such as an UUID.
• Set the JWT expiry (exp) claim so that the lifetime of the token is reasonably low.
  • Tokendings allows a maximum lifetime of 120 seconds.
  • A lifetime between 10-30 seconds should be fine for most situations.

Example Client Assertion Values

Header

{
  "kid": "93ad09a5-70bc-4858-bd26-5ff4a0c5f73f",
  "typ": "JWT",
  "alg": "RS256"
}

Payload

{
  "sub": "prod-gcp:namespace-gcp:gcp-app",
  "aud": "https://tokendings.prod-gcp.nais.io/token",
  "nbf": 1592508050,
  "iss": "prod-gcp:namespace-gcp:gcp-app",
  "exp": 1592508171,
  "iat": 1592508050,
  "jti": "fd9717d3-6889-4b22-89b8-2626332abf14"
}

Exchanging a token

In order to acquire a token from Tokendings that is properly scoped to a given target application, you must exchange an existing subject token (i.e. a token that contains a subject, in this case a citizen end-user).

Tokendings will then issue an access_token in JWT format, based on the parameters set in the token request. The token can then be used as a Bearer token in the Authorization header when calling your target API on behalf of the aforementioned subject.

Prerequisites

• You have a subject token in the form of an access_token issued by one of the following providers:
  • ID-porten
  • Tokendings
  • Loginservice (Remember that loginservice is a deprecated legacy system. TokenX currently accepts these tokens during the grace period for migration.)
• You have a client assertion that authenticates your application.

Exchange Request

The following denotes the required parameters needed to perform an exchange request.

Parameter	Value	Comment
grant_type	urn:ietf:params:oauth:grant-type:token-exchange	The identifier of the OAuth 2.0 grant to use, in this case the OAuth 2.0 Token Exchange grant. This grants allows applications to exchange one token for a new one containing much of the same information while still being correctly "scoped" in terms of OAuth.
client_assertion_type	urn:ietf:params:oauth:client-assertion-type:jwt-bearer	Identifies the type of assertion the client/application will use to authenticate itself to Tokendings, in this case a JWT.
client_assertion	A serialized JWT identifying the calling app	The client assertion; a JWT signed by the calling client/application used to identify said client/application.
subject_token_type	urn:ietf:params:oauth:token-type:jwt	Identifies the type of token that will be exchanged with a new one, in this case a JWT
subject_token	A serialized JWT, the token that should be exchanged	The actual token (JWT) containing the signed-in user. Should be an access_token.
audience	The identifier of the app you wish to use the token for	Identifies the intended audience for the resulting token, i.e. the target app you request a token for. This value shall be the client_id of the target app using the naming scheme <cluster>:<namespace>:<appname> e.g. prod-fss:namespace1:app1

The request should then sent to the token_endpoint of Tokendings, the value of which exists in the metadata found at the well-known endpoint.

Example

POST /token HTTP/1.1
Host: tokendings.prod-gcp.nais.io
Content-Type: application/x-www-form-urlencoded

grant_type=urn:ietf:params:oauth:grant-type:token-exchange&
client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer&
client_assertion=eY...............&
subject_token_type=urn:ietf:params:oauth:token-type:jwt&
subject_token=eY...............&
audience=prod-fss:namespace1:app1

Exchange Response

Tokendings will respond with a JSON object

Example

{
  "access_token" : "eyJraWQiOi..............",
  "issued_token_type" : "urn:ietf:params:oauth:token-type:access_token",
  "token_type" : "Bearer",
  "expires_in" : 899
}

If performance is a concern, the token can be cached for reuse within the validity period indicated by the expires_in field.

Exchange Error Response

If the exchange request is invalid, Tokendings will respond with a structured error, as specified in RFC 8693, Section 2.2.2:

Example

{
    "error_description" : "token exchange audience <some-audience> is invalid",
    "error" : "invalid_request"
}

Token Validation

If your app is a resource server / API and receives a token from another application, it is your responsibility to validate the token intended for your application.

Configure your app with the OAuth 2.0 Authorization Server Metadata from the well-known endpoint. This contains the issuer name and JWKS endpoint containing the authorization server's public keys.

Signature Verification

• The token should be signed with the RS256 algorithm (defined in JWT header). Tokens not matching this algorithm should be rejected.
• Verify that the signature is correct.
• The issuer's signing keys can be retrieved from the JWK Set (JWKS) at the jwks_uri.
• The kid attribute in the token header is thus a reference to a key contained within the JWK Set.
• The token signature should be verified against the public key in the matching JWK.

Claims

The following claims are by default provided in the issued token and should explicitly be validated:

• iss (issuer): The issuer of the token, the Tokendings issuer URI must match exactly.
• aud (audience): The intended audience for the token, must match your application's client_id.
• exp (expiration time): Expiration time, i.e. tokens received after this date must be rejected.
• nbf (not before time): The token cannot be used before this time, i.e. if the token is issued in the "future" (outside "reasonable" clock skew) it must be rejected.
• iat (issued at time): The time at which the token has been issued. Must be before exp.
• sub (subject): If applicable, used in user centric access control. This represents a unique identifier for the user.

Other non-standard claims in the token are copied verbatim from the original token issued by idp. For example, the claim used for the national identity number (fødselsnummer) for tokens issued by ID-porten is pid.

To extract such non-standard information from tokens, first use the idp claim to find the original token issuer. You can then map the original issuer's preferred claims to the claims in tokens issued by TokenX.

Example Token (exchanged from ID-porten)

The following example shows the claims of a token issued by Tokendings, where the exchanged subject token is issued by ID-porten:

Example

{
  "at_hash": "x6lQGCdbMX62p1VHeDsFBA",
  "sub": "HmjqfL7....",
  "amr": [
    "BankID"
  ],
  "iss": "https://tokendings.prod-gcp.nais.io",
  "pid": "12345678910",
  "locale": "nb",
  "client_id": "prod-gcp:team-a:app-a",
  "sid": "DASgLATSjYTp__ylaVbskHy66zWiplQrGDAYahvwk1k",
  "aud": "prod-fss:team-b:app-b",
  "acr": "Level4",
  "nbf": 1597783152,
  "idp": "https://oidc.difi.no/idporten-oidc-provider/",
  "auth_time": 1611926877,
  "exp": 1597783452,
  "iat": 1597783152,
  "jti": "97f580a6-b479-426d-876b-267aa9848e2e"
}

---

Last update: 2022-11-16
Created: 2020-08-18