Istio is an open source service mesh for managing the different microservices that make up a cloud-native application. Istio provides a mechanism to customize the Envoy configuration generated by Istio Pilot using EnvoyFilter.

This tutorial shows how Istio’s EnvoyFilter can be configured to include Envoy’s External Authorization filter to delegate authorization decisions to OPA.

Prerequisites

This tutorial requires Kubernetes 1.20 or later. To run the tutorial locally ensure you start a cluster with Kubernetes version 1.20+, we recommend using minikube or KIND.

The tutorial also requires Istio v1.8.0 or later. It assumes you have Istio deployed on top of Kubernetes. See Istio’s Quick Start page to get started.

Steps

1. Install OPA-Envoy

kubectl apply -f https://raw.githubusercontent.com/open-policy-agent/opa-envoy-plugin/main/examples/istio/quick_start.yaml

The quick_start.yaml manifest defines the following resources:

• External Authorization Filter to direct authorization checks to the OPA-Envoy sidecar. See kubectl -n istio-system get envoyfilter ext-authz for details.

• Kubernetes namespace (opa-istio) for OPA-Envoy control plane components.

• Kubernetes admission controller in the opa-istio namespace that automatically injects the OPA-Envoy sidecar into pods in namespaces labelled with opa-istio-injection=enabled.

• OPA configuration file and an OPA policy into ConfigMaps in the namespace where the app will be deployed, e.g., default. The following is the example OPA policy:

  • alice is granted a guest role and can perform a GET request to /productpage.
  • bob is granted an admin role and can perform a GET to /productpage and /api/v1/products.
  

  package istio.authz
  
  import input.attributes.request.http as http_request
  import input.parsed_path
  
  default allow = false
  
  allow {
      parsed_path[0] == "health"
      http_request.method == "GET"
  }
  
  allow {
      roles_for_user[r]
      required_roles[r]
  }
  
  roles_for_user[r] {
      r := user_roles[user_name][_]
  }
  
  required_roles[r] {
      perm := role_perms[r][_]
      perm.method == http_request.method
      perm.path == http_request.path
  }
  
  user_name = parsed {
      [_, encoded] := split(http_request.headers.authorization, " ")
      [parsed, _] := split(base64url.decode(encoded), ":")
  }
  
  user_roles := {
      "alice": ["guest"],
      "bob": ["admin"]
  }
  
  role_perms := {
      "guest": [
          {"method": "GET",  "path": "/productpage"},
      ],
      "admin": [
          {"method": "GET",  "path": "/productpage"},
          {"method": "GET",  "path": "/api/v1/products"},
      ],
  }

  OPA is configured to query for the data.istio.authz.allow decision. If the response is true the operation is allowed, otherwise the operation is denied. Sample input received by OPA is shown below:

  

  data.istio.authz.allow

  

  {
      "attributes": {
          "request": {
              "http": {
                  "method": "GET",
                  "path": "/productpage",
                  "headers": {
                      "authorization": "Basic YWxpY2U6cGFzc3dvcmQ="
                  }
              }
          }
      }
  }

  With the input value above, the answer is:

  

  true

  An example of the complete input received by OPA can be seen here.

  In typical deployments the policy would either be built into the OPA container image or it would fetched dynamically via the Bundle API. ConfigMaps are used in this tutorial for test purposes.

2. Enable automatic injection of the Istio Proxy and OPA-Envoy sidecars in the namespace where the app will be deployed, e.g., default

kubectl label namespace default opa-istio-injection="enabled"
kubectl label namespace default istio-injection="enabled"

3. Deploy the BookInfo application and make it accessible outside the cluster

kubectl apply -f https://raw.githubusercontent.com/istio/istio/master/samples/bookinfo/platform/kube/bookinfo.yaml

kubectl apply -f https://raw.githubusercontent.com/istio/istio/master/samples/bookinfo/networking/bookinfo-gateway.yaml

4. Set the GATEWAY_URL environment variable in your shell to the public IP/port of the Istio Ingress gateway

minikube:

export INGRESS_PORT=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="http2")].nodePort}')
export INGRESS_HOST=$(minikube ip)
export GATEWAY_URL=$INGRESS_HOST:$INGRESS_PORT
echo $GATEWAY_URL

minikube (example):

192.168.99.100:31380

For other platforms see the Istio documentation on determining ingress IP and ports.

5. Exercise the OPA policy

Check that alice can access /productpage BUT NOT /api/v1/products.

curl --user alice:password -i http://$GATEWAY_URL/productpage
curl --user alice:password -i http://$GATEWAY_URL/api/v1/products

Check that bob can access /productpage AND /api/v1/products.

curl --user bob:password -i http://$GATEWAY_URL/productpage
curl --user bob:password -i http://$GATEWAY_URL/api/v1/products

Wrap Up

Congratulations for finishing the tutorial !

This tutorial showed how Istio’s EnvoyFilter can be configured to use OPA as an External authorization service.

This tutorial also showed a sample OPA policy that returns a boolean decision to indicate whether a request should be allowed or not.

More details about the tutorial can be seen here.