istio

Overview

OPA-Envoy extends OPA with a gRPC server that implements the Envoy External Authorization API. You can use this version of OPA to enforce fine-grained, context-aware access control policies at the Istio Proxy layer without modifying your microservice.

How does it work?

In addition to the Istio Proxy/Envoy sidecar, your application pods will include an OPA sidecar. When Istio Proxy receives API requests destined for your microservice, it checks with OPA to decide if the request should be allowed.

Evaluating policies locally at the Istio Proxy layer is preferable because it avoids introducing a network hop (which has implications on performance and availability) in order to perform the authorization check.

Quick Start

This section assumes you are testing with Istio v1.8.0 or later.

This section assumes you have Istio deployed on top of Kubernetes. See Istio's Quick Start page to get started.

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.

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 sample 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

6. Exercise the sample policy. 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

Controlling the injection policy at the pod level

If you want to control the injection policy at the pod level, set the sidecar.opa-istio.io/inject label to false on the pod. An example of the updated admission controller configuration is shown below:

objectSelector:
  matchExpressions:
  - key: sidecar.opa-istio.io/inject
    operator: NotIn
    values:
    - "false"

Example Bundle Configuration

In the Quick Start section an OPA policy is loaded via a volume-mounted ConfigMap. For production deployments, we recommend serving policy Bundles from a remote HTTP server.

Using the configuration shown below, OPA will download a sample bundle from https://www.openpolicyagent.org. The sample bundle contains the exact same policy that was loaded into OPA via the volume-mounted ConfigMap. More details about this policy can be found in the Example Policy section.

config.yaml:

services:
  - name: controller
    url: https://www.openpolicyagent.org
bundles:
  istio/authz:
    service: controller
plugins:
    envoy_ext_authz_grpc:
        addr: :9191
        path: istio/authz/allow
        dry-run: false
        enable-reflection: false

You can download the bundle and inspect it yourself:

mkdir example && cd example
curl -s -L https://www.openpolicyagent.org/bundles/istio/authz | tar xzv

To allow OPA to access the sample bundle from https://www.openpolicyagent.org, create a ServiceEntry as shown below:

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: opa-bundle
spec:
  hosts:
   - www.openpolicyagent.org
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  resolution: DNS
  location: MESH_EXTERNAL
EOF

In this way OPA can periodically download bundles of policy from an external server and hence loading the policy via a volume-mounted ConfigMap would not be required. The readinessProbe to GET /health?bundles ensures that the OPA-Envoy sidecar container becomes ready after the bundles are activated.

Example Policy

The following OPA policy is used in the Quick Start section above. This policy restricts access to the BookInfo such that:

• Alice is granted a guest role and can access the /productpage frontend BUT NOT the /v1/api/products backend.
• Bob is granted an admin role and can access the /productpage frontend AND the /v1/api/products backend.

package istio.authz

import input.attributes.request.http as http_request
import input.parsed_path

default allow = false

allow {
    roles_for_user[r]
    required_roles[r]
}

# allow health checks of the opa sidecar
allow {
    parsed_path[0] == "health"
    http_request.method == "GET"
}

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"},
    ],
}

Example Input

The input value defined for your policy will resemble the JSON below:

{
  "parsed_path": ["api", "v1", "products"],
  "parsed_query": {"lang": ["en"]},
  "parsed_body":  {"id": "ext1", "name": "opa_authz"},
  "attributes": {
    "source": {
      "address": {
        "Address": {
          "SocketAddress": {
            "address": "172.17.0.10",
            "PortSpecifier": {
              "PortValue": 36472
            }
          }
        }
      }
    },
    "destination": {
      "address": {
        "Address": {
          "SocketAddress": {
            "address": "172.17.0.17",
            "PortSpecifier": {
              "PortValue": 9080
            }
          }
        }
      }
    },
    "request": {
      "http": {
        "id": "13359530607844510314",
        "method": "GET",
        "headers": {
          ":authority": "192.168.99.100:31380",
          ":method": "GET",
          ":path": "/api/v1/products?lang=en",
          "accept": "*/*",
          "authorization": "Basic YWxpY2U6cGFzc3dvcmQ=",
          "content-length": "0",
          "user-agent": "curl/7.54.0",
          "x-b3-sampled": "1",
          "x-b3-spanid": "537f473f27475073",
          "x-b3-traceid": "537f473f27475073",
          "x-envoy-internal": "true",
          "x-forwarded-for": "172.17.0.1",
          "x-forwarded-proto": "http",
          "x-istio-attributes": "Cj4KE2Rlc3RpbmF0aW9uLnNlcnZpY2USJxIlcHJvZHVjdHBhZ2UuZGVmYXVsdC5zdmMuY2x1c3Rlci5sb2NhbApPCgpzb3VyY2UudWlkEkESP2t1YmVybmV0ZXM6Ly9pc3Rpby1pbmdyZXNzZ2F0ZXdheS02Nzk5NWM0ODZjLXFwOGpyLmlzdGlvLXN5c3RlbQpBChdkZXN0aW5hdGlvbi5zZXJ2aWNlLnVpZBImEiRpc3RpbzovL2RlZmF1bHQvc2VydmljZXMvcHJvZHVjdHBhZ2UKQwoYZGVzdGluYXRpb24uc2VydmljZS5ob3N0EicSJXByb2R1Y3RwYWdlLmRlZmF1bHQuc3ZjLmNsdXN0ZXIubG9jYWwKKgodZGVzdGluYXRpb24uc2VydmljZS5uYW1lc3BhY2USCRIHZGVmYXVsdAopChhkZXN0aW5hdGlvbi5zZXJ2aWNlLm5hbWUSDRILcHJvZHVjdHBhZ2U=",
          "x-request-id": "92a6c0f7-0250-944b-9cfc-ae10cbcedd8e"
        },
        "path": "/api/v1/products?lang=en",
        "host": "192.168.99.100:31380",
        "protocol": "HTTP/1.1",
        "body": "{\"id\": \"ext1\", \"name\": \"opa_authz\"}"
      }
    }
  }
}

The parsed_path field in the input is generated from the path field in the HTTP request which is included in the Envoy External Authorization CheckRequest message type. This field provides the request path as a string array which can help policy authors perform pattern matching on the HTTP request path. The below sample policy allows anyone to access the path /api/v1/products.

package istio.authz

default allow = false

allow {
   input.parsed_path = ["api", "v1", "products"]
}

The parsed_query field in the input is also generated from the path field in the HTTP request. This field provides the HTTP url query as a map of string array. The below sample policy allows anyone to access the path /api/v1/products?lang=en&id=1&id=2.

package istio.authz

default allow = false

allow {
   input.parsed_path = ["api", "v1", "products"]
   input.parsed_query.lang = ["en"]
   input.parsed_query.id = ["1", "2"]
}

The parsed_body field in the input is generated from the body field in the HTTP request which is included in the Envoy External Authorization CheckRequest message type. This field contains the deserialized JSON request body which can then be used in a policy as shown below.

package istio.authz

default allow = false

allow {
   input.parsed_body.id == "ext1"
   input.parsed_body.name == "opa_authz"
}