OPA

About OPA

OPA is an open source, general-purpose policy engine that you can use to enforce versatile policies in a uniform way across your organization. Compared to a role-based access control (RBAC) authorization system, OPA allows you to create more fine-grained policies. For more information, see the OPA docs.

OPA policies are written in Rego. Based on the older query languages Prolog and Datalog, Rego extends support to more modern document models such as JSON.

Gloo Mesh's OPA integration populates an input document to use in your OPA policies. The structure of the input document depends on the context of the incoming request, described in the following table.

Before you begin

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 Platform CLI, meshctl, 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.

   kubectl get pods --context ${REMOTE_CONTEXT1} -A -l app=ext-auth-service
   

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.

   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 --context ${REMOTE_CONTEXT1} -n bookinfo create configmap allow-get-users --from-file=policy.rego
   

3. Create an external auth server to use for your policy. The following example refers directly to the default Gloo Mesh external auth service, but you can also use a virtual destination instead. For more information, see External auth server setup.

   kubectl --context ${REMOTE_CONTEXT1} 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: $REMOTE_CLUSTER1
         name: ext-auth-service
         namespace: gloo-mesh-addons
   EOF
   

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

   When you create the policy with a destination selector, only Kubernetes services can be specified in the applyToDestination section. Gloo virtual destinations or Gloo external services are not supported.

   kubectl --context ${REMOTE_CONTEXT1} apply -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 OPA 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.

   • Kubernetes 1.22 or earlier
   • Kubernetes 1.23 or later

   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, as shown in the other tab.

   1. Create the curl pod.

      kubectl run -it -n bookinfo --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
      

   Use the kubernetes debug command to create an ephemeral curl container in the deployment. This way, the curl container inherits any permissions from the app that you want to test. If you don't run Kubernetes 1.23 or later, you can deploy a separate curl pod or manually add the curl container as shown in the other tab.

   kubectl --context ${REMOTE_CONTEXT1} -n bookinfo debug -i pods/$(kubectl get pod --context ${REMOTE_CONTEXT1} -l app=reviews -A -o jsonpath='{.items[0].metadata.name}') --image=curlimages/curl -- curl -v http://ratings:9080/ratings/1
   

   If the output has an error about EphemeralContainers, see Ephemeral containers don’t work when testing Bookinfo.

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

   • Kubernetes 1.22 or earlier
   • Kubernetes 1.23 or later

   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, as shown in the other tab.

   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
      

   Use the kubernetes debug command to create an ephemeral curl container in the deployment. This way, the curl container inherits any permissions from the app that you want to test. If you don't run Kubernetes 1.23 or later, you can deploy a separate curl pod or manually add the curl container as shown in the other tab.

   kubectl --context ${REMOTE_CONTEXT1} -n bookinfo debug -i pods/$(kubectl get pod --context ${REMOTE_CONTEXT1} -l app=reviews -A -o jsonpath='{.items[0].metadata.name}') --image=curlimages/curl -- curl -v -X GET http://ratings:9080/ratings/2
   

   You can reach the ratings app again!

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

3. Optional: Clean up the resources that you created.

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