By default, the Gloo external auth service is enabled to use an OPA module. You can create your Rego rules as Kubernetes config maps in the cluster for more fine-grained access control. Then, you use an external auth policy to tell the Gloo external auth service to load these rules via the OPA module. This approach can be convenient for quick testing or small OPA use cases.

Other OPA options:

  • You can still load Rego rules with a Kubernetes config map to the Gloo external auth service even when you use other OPA server methods.
  • You also get the OPA-Envoy plugin API with the Gloo external auth service.
  • Bring your own OPA server for extended OPA capabilities such as bundling.
  • Instead of bringing your own server, you can deploy an OPA server as a sidecar to the Gloo external auth service.

Before you begin

  1. Set up Gloo Mesh Gateway in a single cluster.
  2. Install Bookinfo and other sample apps.

  3. Configure an HTTP listener on your gateway and set up basic routing for the sample apps.

  4. Make sure that the external auth service is installed and running. If not, install the external auth service in your Gloo environment.

      kubectl get pods  -A -l app=ext-auth-service

  5. Get the external address of your ingress gateway. The steps vary depending on the type of load balancer that backs the ingress gateway.

 ```shell
 export INGRESS_GW_ADDRESS=$(kubectl get svc -n gloo-mesh-gateways istio-ingressgateway -o jsonpath="{.status.loadBalancer.ingress[0]['hostname','ip']}")
 echo $INGRESS_GW_ADDRESS
 ```

Note: Depending on your environment, you might see <pending> instead of an external IP address. For example, if you are testing locally in kind or minikube, or if you have insufficient permissions in your cloud platform, you can instead port-forward the service port of the ingress gateway:

  kubectl -n gloo-mesh-gateways port-forward deploy/istio-ingressgateway-1-18 8081

Configure an external auth policy with OPA

Create the external auth policy with OPA.

  1. Create an OPA Rego policy file.

      cat <<EOF > policy.rego
package test

default allow = false
allow {
    startswith(input.http_request.path, "/ratings/2")
    input.http_request.method == "GET"
}
allow {
    input.http_request.path == "/ratings/3"
    any({input.http_request.method == "GET",
        input.http_request.method == "DELETE"
    })
}
EOF
    Review the following table to understand this configuration.
    SettingDescription
    default allow = falseDenies all requests by default.
    allow {...}Allows requests that match two conditions as follows. 1) The path starts with /ratings/2 AND the HTTP method is GET; or, 2) the path is exactly /ratings/3 AND the HTTP method is either GET or DELETE.

  2. Store the OPA policy in a Kubernetes config map in the workload cluster that you want to create the external auth policy in.

      kubectl -n bookinfo create configmap allow-get-users --from-file=policy.rego

  3. Create an external auth server to use for your policy.

      kubectl apply  -f - <<EOF
apiVersion: admin.gloo.solo.io/v2
kind: ExtAuthServer
metadata:
  name: ext-auth-server
  namespace: bookinfo
spec:
  destinationServer:
    port:
      number: 8083
    ref:
      cluster: $CLUSTER_NAME
      name: ext-auth-service
      namespace: gloo-mesh
EOF

  4. Create an external auth policy that uses the OPA config map.

      kubectl apply -f - <<EOF
apiVersion: security.policy.gloo.solo.io/v2
kind: ExtAuthPolicy
metadata:
  name: ratings-opa
  namespace: bookinfo
spec:
  applyToRoutes:
  - route:
      labels:
        route: ratings
  config:
    server:
      name: ext-auth-server
      namespace: bookinfo
      cluster: $CLUSTER_NAME
    glooAuth:
      configs:
      - opaAuth:
          modules:
          - name: allow-get-users
            namespace: bookinfo
          query: "data.test.allow == true"
EOF

    Review the following table to understand this configuration. For more information, see the API reference.

    SettingDescription
    applyToRoutesUse labels to configure which routes to apply the policy to. This example label matches the app and route from the example route table that you apply separately. If omitted and you do not have another selector such as applyToDestinations, the policy applies to all routes in the workspace.
    serverThe external auth server to use for the policy.
    opaAuthConfigure the OPA authentication details.
    modulesRefer to the name and namespace of the config map that has the OPA policy. Then, Gloo can use the OPA policy to use to resolve the query. This example uses the config map that you previously created.
    queryThe query that determines the authentication decision. The result of this query must be either a boolean or an array with a boolean as the first element. A value of true means that the request is authorized. Any other value or error means that the request is denied. In this example, data.test.allow is set to true. data is the section in the config map. test.allow are part of the OPA policy that you previously created. Access is allowed only if the response meets the allow conditions in the policy.

Verify the external auth API key policy

  1. Send a request to the ratings app along a path that is not allowed by the OPA policy, such as /ratings/1. Now, the request is blocked with a 403 response.

    • HTTP:
        curl -vik --resolve www.example.com:80:${INGRESS_GW_IP} http://www.example.com:80/ratings/1
    • HTTPS:
        curl -vik --resolve www.example.com:443:${INGRESS_GW_IP} https://www.example.com:443/ratings/1

  2. Send the request again, this time along a path that is allowed by the OPA policy, such as GET /ratings/2.

    • HTTP:
        curl -vik -X GET --resolve www.example.com:80:${INGRESS_GW_IP} http://www.example.com:80/ratings/2
    • HTTPS:
        curl -vik -X GET --resolve www.example.com:443:${INGRESS_GW_IP} https://www.example.com:443/ratings/2

    You can reach the ratings app again!

      {"id":1,"ratings":{"Reviewer1":5,"Reviewer2":4}}

Cleanup

You can optionally remove the resources that you set up as part of this guide.
  kubectl -n bookinfo delete ConfigMap allow-get-users 
kubectl -n bookinfo delete ExtAuthPolicy ratings-opa 
kubectl -n bookinfo delete ExtAuthServer ext-auth-server