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opa-istio-plugin

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This repository contains an extended version of OPA (OPA-Istio) that allows you to enforce OPA policies at the Istio Proxy layer.

Issue Management

Use OPA GitHub Issues to request features or file bugs.

Overview

OPA-Istio 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.

arch

Quick Start

This section assumes you are testing with Istio v1.1.0 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-Istio.

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

    The quick_start.yaml manifest defines the following resources:

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

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

    • Kubernetes admission controller in the opa-istio namespace that automatically injects the OPA-Istio 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-Istio 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

Configuration

To deploy OPA-Istio include the following container in your Kubernetes Deployments:

containers:
- image: openpolicyagent/opa:0.15.1-istio
  imagePullPolicy: IfNotPresent
  name: opa-istio
  volumeMounts:
  - mountPath: /config
    name: opa-istio-config
  args:
  - run
  - --server
  - --config-file=/config/config.yaml

The OPA-Istio configuration file should be volume mounted into the container. Add the following volume to your Kubernetes Deployments:

volumes:
- name: opa-istio-config
  configMap:
    name: opa-istio-config

The OPA-Istio plugin supports the following configuration fields:

Field Required Description
plugins["envoy_ext_authz_grpc"].addr No Set listening address of Envoy External Authorization gRPC server. This must match the value configured in the Envoy Filter resource. Default: :9191.
plugins["envoy_ext_authz_grpc"].query No Specifies the name of the policy decision to query. The policy decision can either be a boolean or an object. If boolean, true indicates the request should be allowed and false indicates the request should be denied. If the policy decision is an object, it must contain the allowed key set to either true or false to indicate if the request is allowed or not respectively. It can optionally contain a headers field to send custom headers to the downstream client or upstream. An optional body field can be included in the policy decision to send a response body data to the downstream client. Also an optional http_status field can be included to send a HTTP response status code to the downstream client other than 403 (Forbidden). Default: data.istio.authz.allow.
plugins["envoy_ext_authz_grpc"].dry-run No Configures the Envoy External Authorization gRPC server to unconditionally return an ext_authz.CheckResponse.Status of google_rpc.Status{Code: google_rpc.OK}. Default: false.
plugins["envoy_ext_authz_grpc"].enable-reflection No Enables gRPC server reflection on the Envoy External Authorization gRPC server. Default: false.

If the configuration does not specify the query field, data.istio.authz.allow will be considered as the default name of the policy decision to query.

The dry-run parameter is provided to enable you to test out new policies. You can set dry-run: true which will unconditionally allow requests. Decision logs can be monitored to see what "would" have happened. This is especially useful for initial integration of OPA or when policies undergo large refactoring.

The enable-reflection parameter registers the Envoy External Authorization gRPC server with reflection. After enabling server reflection, a command line tool such as grpcurl can be used to invoke RPC methods on the gRPC server. See gRPC Server Reflection Usage section for more details.

An example of a rule that returns an object that not only indicates if a request is allowed or not but also provides optional response headers, body and HTTP status that can be sent to the downstream client or upstream can be seen below in the Example Policy with Object Response section.

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
        query: data.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.

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

default allow = false

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"},
    ],
}

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"
}

Example Policy with Object Response

The allow rule in the below policy when queried generates an object that provides the status of the request (ie. allowed or denied) alongwith some headers, body data and HTTP status which will be included in the response that is sent back to the downstream client or upstream.

package istio.authz

default allow = {
  "allowed": false,
  "headers": {"x-ext-auth-allow": "no"},
  "body": "Unauthorized Request",
  "http_status": 301
}

allow = response {
  input.attributes.request.http.method == "GET"
  response := {
    "allowed": true,
    "headers": {"x-ext-auth-allow": "yes"}
  }
}

Example with JWT payload passed from Envoy

Envoy can be configured to pass validated JWT payload data into the ext_authz filter with metadata_context_namespaces and payload_in_metadata.

Example Envoy Configuration

http_filters:
- name: envoy.filters.http.jwt_authn
  typed_config:
  "@type": type.googleapis.com/envoy.config.filter.http.jwt_authn.v2alpha.JwtAuthentication
  providers:
    example:
      payload_in_metadata: verified_jwt
      <...>
- name: envoy.ext_authz
  config:
    metadata_context_namespaces:
    - envoy.filters.http.jwt_authn
    <...>

Example OPA Input

This will result in something like the following dictionary being added to input.attributes (some common fields have been excluded for brevity):

"metadata_context": {
  "filter_metadata": {
    "envoy.filters.http.jwt_authn": {
      "fields": {
        "verified_jwt": {
          "Kind": {
            "StructValue": {
              "fields": {
                "email": {
                  "Kind": {
                    "StringValue": "alice@example.com"
                  }
                },
                "exp": {
                  "Kind": {
                    "NumberValue": 1569026124
                  }
                },
                "name": {
                  "Kind": {
                    "StringValue": "Alice"
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

Example OPA Policy

This JWT data can be accessed in OPA policy like this:

jwt_payload = _value {
    verified_jwt := input.attributes.metadata_context.filter_metadata["envoy.filters.http.jwt_authn"]["fields"]["verified_jwt"]
    _value := {
        "name": verified_jwt["Kind"]["StructValue"]["fields"]["name"]["Kind"]["StringValue"],
        "email": verified_jwt["Kind"]["StructValue"]["fields"]["email"]["Kind"]["StringValue"]
    }
}

allow {
  jwt_payload.email == "alice@example.com"
}

gRPC Server Reflection Usage

This section provides examples of interacting with the Envoy External Authorization gRPC server using the grpcurl tool.

  • List all services exposed by the server

    $ grpcurl -plaintext localhost:9191 list

    Output:

    envoy.service.auth.v2.Authorization
    grpc.reflection.v1alpha.ServerReflection
  • Invoke RPC on the server

    $ grpcurl -plaintext -import-path ./proto/ -proto ./proto/envoy/service/auth/v2/external_auth.proto -d '
    {
      "attributes": {
        "request": {
          "http": {
            "method": "GET",
            "path": "/api/v1/products"
          }
        }
      }
    }' localhost:9191 envoy.service.auth.v2.Authorization/Check

    Output:

    {
      "status": {
        "code": 0
    },
      "okResponse": {
        "headers": [
          {
            "header": {
              "key": "x-ext-auth-allow",
              "value": "yes"
            }
          }
        ]
      }
    }

The -proto and -import-path flags tell grpcurl the relevant proto source file and the folder from which dependencies can be imported respectively. These flags need to be provided as the Envoy External Authorization gRPC server does not support reflection. See this issue for details.

Dependencies

Dependencies are managed with Modules. If you need to add or update dependencies, modify the go.mod file or use go get. More information is available here. Finally commit all changes to the repository.

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