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.

OPA input structureDescription
input.check_requestBy default, all OPA policies contain an Envoy Auth Service CheckRequest. This object has all the information that Envoy gathers about the request being processed. You can view the structure of this object in the attributes section of the linked Envoy doc.
input.http_requestWhen processing an HTTP request, Envoy populates this field for convenience. For the structure of this object, see the Envoy HttpRequest docs and proto files.
input.state.jwtIf you use OAuth, the token retrieved during the OIDC flow is placed into this field.

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 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

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"
    Review the following table to understand this configuration.
    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 --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
      name: ext-auth-server
      namespace: bookinfo
          number: 8083
          cluster: $REMOTE_CLUSTER1
          name: ext-auth-service
          namespace: gloo-mesh-addons
  4. Create an external auth policy that uses the OPA config map.

    kubectl --context ${REMOTE_CONTEXT1} apply -f - <<EOF
    apiVersion: security.policy.gloo.solo.io/v2
    kind: ExtAuthPolicy
      name: ratings-opa
      namespace: bookinfo
      - selector:
            app: ratings
          name: ext-auth-server
          namespace: bookinfo
          cluster: $REMOTE_CLUSTER1
          - opaAuth:
              - name: allow-get-users
                namespace: bookinfo
              query: "data.test.allow == true"

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

applyToDestinationsConfigure which destinations to apply the policy to, by using labels. Destinations can be a Kubernetes service, VirtualDestination, or ExternalService. If you do not specify any destinations or routes, the policy applies to all destinations in the workspace by default. If you do not specify any destinations but you do specify a route, the policy applies to the route but to no destinations.
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 Mesh 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 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.

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

    You can reach the ratings app again!

  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