OPA with Rego rules in config maps

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.
• 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 link

1. Complete the multicluster getting started guide to set up the following testing environment.

   • Three clusters along with environment variables for the clusters and their Kubernetes contexts.
   • The Gloo meshctl CLI, along with other CLI tools such as kubectl and istioctl.
   • The Gloo management server in the management cluster, and the Gloo agents in the workload clusters.
   • Istio installed in the workload clusters.
   • A simple Gloo workspace setup.
2. Install Bookinfo and other sample apps.

3. 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 --context $REMOTE_CONTEXT1  -A -l app=ext-auth-service
     

Configure an external auth policy with OPA link

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.

   Setting	Description
   default allow = false	Denies 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 --context $REMOTE_CONTEXT1 
     

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

     kubectl apply --context $REMOTE_CONTEXT1  -f - <<EOF
   apiVersion: admin.gloo.solo.io/v2
   kind: ExtAuthServer
   metadata:
     name: ext-auth-server
     namespace: bookinfo
   spec:
     destinationServer:
       port:
         number: 8083
       ref:
         cluster: $REMOTE_CLUSTER1
         name: ext-auth-service
         namespace: gloo-mesh
   EOF
     

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

  kubectl apply --context ${REMOTE_CONTEXT1} -f - <<EOF
apiVersion: security.policy.gloo.solo.io/v2
kind: ExtAuthPolicy
metadata:
  name: ratings-opa
  namespace: bookinfo
spec:
  applyToDestinations:
  - selector:
      labels:
        app: ratings
  config:
    server:
      name: ext-auth-server
      namespace: bookinfo
      cluster: $REMOTE_CLUSTER1
    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.

Verify the external auth API key policy link

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.Create a temporary curl pod in the bookinfo namespace, so that you can test the app setup. You can also use this method in Kubernetes 1.23 or later, but an ephemeral container might be simpler.

   1. Create the curl pod.

        kubectl run -it -n httpbin --context ${REMOTE_CONTEXT1} curl --image=curlimages/curl:7.73.0 --rm  -- sh
        

   2. Send a request to the ratings app.

        curl http://ratings:9080/ratings/1 -v
        

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

   1. Send a request to the ratings app.

        curl -v -X GET http://ratings:9080/ratings/2
        

   2. Exit the temporary pod. The pod deletes itself.

        exit
        

   You can reach the ratings app again!

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

Cleanup link

  kubectl -n bookinfo delete ConfigMap allow-get-users --context $REMOTE_CONTEXT1 
kubectl -n bookinfo delete ExtAuthPolicy ratings-opa --context $REMOTE_CONTEXT1 
kubectl -n bookinfo delete ExtAuthServer ext-auth-server --context $REMOTE_CONTEXT1