nginx-subrequest-auth-jwt

nginx-subrequest-auth-jwt

This project implements a simple JWT validation endpoint meant to be used with NGINX's subrequest authentication, and specifically work well with the Kubernetes NGINX Ingress Controller external auth annotations.

It validates a JWT token passed in the Authorization header against a configured public key, and further validates that the JWT contains appropriate claims.

Limitations

The configuration format currently only supports a single elliptic curve public key for signature validation, and does not have a facility for rotating keys without restart. Basic support in the configuration format for supporting multiple active keys, and of different types, at once is in place but currently not used.

Configuration

A number of flags affect how the service is started:

Configuration file

The service takes a configuration file in YAML format, by default config.yaml. For example:

validationKeys:
  - type: ecPublicKey
    key: |
      -----BEGIN PUBLIC KEY-----
      ...
      -----END PUBLIC KEY-----
claimsSource: static
claims:
  - group:
      - developers
      - administrators

With this configuration, a JWT will be validated against the given public key, and the claims are then matched against the given structure, meaning there has to be a group claim, with either a developers or administrators value.

Claims can either be statically set, as in the above example, or passed via query string parameters. The claimsSource configuration parameter controls which mode the server operates in, and can be either static or queryString. Further examples of the two modes are given below.

Static

Multiple alternative allowed sets of claims can be configured, for example:

validationKeys:
  - type: ecPublicKey
    key: |
      -----BEGIN PUBLIC KEY-----
      ...
      -----END PUBLIC KEY-----
claims:
  - group:
      - developers
      - administrators
  - deviceClass:
      - server
      - networkEquipment

In this case, the token claims either needs to have the groups as per the previous example, or a deviceClass of server or networkEquipment.

There can also be multiple claims requirements, for example:

validationKeys:
  - type: ecPublicKey
    key: |
      -----BEGIN PUBLIC KEY-----
      ...
      -----END PUBLIC KEY-----
claims:
  - group:
      - developers
      - administrators
    location:
      - hq

Here, the token claims must both have the groups as before, and a location of hq.

Query string

In query string mode, the allowed claims are passed via query string parameters to the /validate endpoint. For example, with /validate?claims_group=developers&claims_group=administrators&claims_location=hq, the token claims must both have a group claim of either developers or administrators, and a location claim of hq.

Each claim must be prefixed with claims_. Giving the same claim multiple time results in any value being accepted.

In this mode, in contrast to static mode, only a single set of acceptable claims can be passed at a time (but different NGINX server blocks can pass different sets).

If no claims are passed in this mode, the request will be denied.

NGINX Ingress Controller integration

To use with the NGINX Ingress Controller, first create a deployment and a service for this endpoint. See the kubernetes/ directory for example manifests. Then on the ingress object you wish to authenticate, add this annotation for a server in static claims source mode:

nginx.ingress.kubernetes.io/auth-url: https://nginx-subrequest-auth-jwt.default.svc.cluster.local:8443/validate

Or, in query string mode:

nginx.ingress.kubernetes.io/auth-url: https://nginx-subrequest-auth-jwt.default.svc.cluster.local:8443/validate?claims_group=developers

Change the url to match the name of the service and namespace you chose when deploying. All requests will now have their JWTs validated before getting passed to the upstream service.

Metrics

This endpoint exposes Prometheus metrics on /metrics:

• http_requests_total{status="<status>"} number of requests handled, by status code (counter)
• nginx_subrequest_auth_jwt_token_validation_time_seconds number of seconds spent validating tokens (histogram)