OPA

Forward request to Open Policy Agent and process the request only if the authorization policy allows for it.

To use this plugin in Konnect Cloud, upgrade your runtimes to at least v2.4.1.1.

Configuration Reference

This plugin is compatible with requests with the following protocols:

• http
• https

This plugin is compatible with DB-less mode.

In DB-less mode, you configure Kong Gateway declaratively. Therefore, the Admin API is mostly read-only. The only tasks it can perform are all related to handling the declarative config, including:

• setting a target's health status in the load balancer
• validating configurations against schemas
• uploading the declarative configuration using the /config endpoint

Enabling the plugin on a service

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$ curl -X POST http://<admin-hostname>:8001/services/<service>/plugins \
    --data "name=opa"  \
    --data "config.opa_host=localhost" \
    --data "config.opa_port=8181" \
    --data "config.opa_path=</v1/data/example/kong/allowBoolean>"

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apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: <opa-example>
config: 
  opa_host: localhost
  opa_port: 8181
  opa_path: </v1/data/example/kong/allowBoolean>
plugin: opa

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apiVersion: v1
kind: Service
metadata:
  name: <service>
  labels:
    app: <service>
  annotations:
    konghq.com/plugins: <opa-example>
spec:
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: <service>
  selector:
    app: <service>

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plugins:
- name: opa
  service: <service>
  config: 
    opa_host: localhost
    opa_port: 8181
    opa_path: </v1/data/example/kong/allowBoolean>

Enabling the plugin on a route

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$ curl -X POST http://<admin-hostname>:8001/routes/<route>/plugins \
    --data "name=opa"  \
    --data "config.opa_host=localhost" \
    --data "config.opa_port=8181" \
    --data "config.opa_path=</v1/data/example/kong/allowBoolean>"

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apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: <opa-example>
config: 
  opa_host: localhost
  opa_port: 8181
  opa_path: </v1/data/example/kong/allowBoolean>
plugin: opa

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apiVersion: networking/v1beta1
kind: Ingress
metadata:
  name: <route>
  annotations:
    kubernetes.io/ingress.class: kong
    konghq.com/plugins: <opa-example>
spec:
  rules:
  - host: examplehostname.com
    http:
      paths:
      - path: /bar
        backend:
          serviceName: echo
          servicePort: 80

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plugins:
- name: opa
  route: <route>
  config: 
    opa_host: localhost
    opa_port: 8181
    opa_path: </v1/data/example/kong/allowBoolean>

Enabling the plugin globally

A plugin which is not associated to any service, route, or consumer is considered global, and will be run on every request. Read the Plugin Reference and the Plugin Precedence sections for more information.

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$ curl -X POST http://<admin-hostname>:8001/plugins/ \
    --data "name=opa"  \
    --data "config.opa_host=localhost" \
    --data "config.opa_port=8181" \
    --data "config.opa_path=</v1/data/example/kong/allowBoolean>"

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apiVersion: configuration.konghq.com/v1
kind: KongClusterPlugin
metadata:
  name: <global-opa>
  annotations:
    kubernetes.io/ingress.class: kong
  labels:
    global: \"true\"
config: 
  opa_host: localhost
  opa_port: 8181
  opa_path: </v1/data/example/kong/allowBoolean>
plugin: opa

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plugins:
- name: opa
  config: 
    opa_host: localhost
    opa_port: 8181
    opa_path: </v1/data/example/kong/allowBoolean>

Parameters

Here's a list of all the parameters which can be used in this plugin's configuration:

Usage

Set up an OPA server

If you are not already running an OPA server, start one by following instructions on openpolicyagent.org.

Set up a dummy policy

Create an example.rego file with the following content:

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package example

default allow = false

allowBoolean {
  header_present
}

header_present {
  input.request.http.headers["my-secret-header"] == "open-sesame"
}

allowDetailed = response {
  header_present
  response := {
    "allow": true,
    "headers": {
      "header-from-opa": "accepted",
    },
  }
}

allowDetailed = response {
  not header_present
  response := {
    "allow": false,
    "status": 418,
    "headers": {
      "header-from-opa": "rejected",
    },
  }
}

This policy allows the request to pass through if it contains the HTTP header my-secret-header with value open-sesame.

Next, configure the policy with OPA:

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curl -XPUT localhost:8181/v1/policies/example --data-binary @example.rego

The above command uses OPA’s default port 8181. It could be different for your setup.

Set up Kong Gateway

Set up a Route and Service in Kong Gateway and then enable the plugin:

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curl -X POST http://<admin-hostname>:8001/routes/<route>/plugins \
    --data "name=opa"  \
    --data "config.opa_path=/v1/data/example/allowBoolean" \
    --data "config.opa_host=<host-where-opa is running>"

Make a request

Now, make a request to Kong Gateway:

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curl http://kong:8000/{proxy_path}

You will get a 403 response from the gateway because OPA has rejected the request.

Next, make the same request providing the necessary header:

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curl http://kong:8000/{proxy_path} \
  -H 'my-secret-header: open-sesame'

This time you will get the response from your upstream service, as this request is allowed by OPA.

Next, update the plugin configuration to use /v1/data/example/allowDetailed as opa_path and observe how the policy affects the response and proxied request.

OPA input structure

The input to OPA has the following JSON structure:

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{
  "input": {
    "request": { # details about the request from client to Kong
      "http": {
        "host": "example.org", # host header used by the client to make the request
        "port": "8000",        # port to which the request was made
        "tls": {},             # TLS details if the request was made on HTTPS and Kong terminated the TLS connection
        "method": "GET",       # HTTP method used in the request
        "scheme": "http",      # protocol used to make the request by the client, this can be either `http` or `https`
        "querystring": {       # Query string in the HTTP request as key-value pairs
          "foo" : "bar",
          "foo2" : "bar2",
        },
        "headers": {           # HTTP headers of the request
          "accept-encoding": "gzip, deflate",
          "connection": "keep-alive",
          "accept": "*\\/*"
        }
      }
    },
    "client_ip": "127.0.0.1",# client IP address as interpreted by Kong
    "service": {             # The Kong service resource to which this request will be forwarded to if OPA allows. Injected only if `include_service_in_opa_input` is set to `true`.
      "host": "httpbin.org",
      "created_at": 1612819937,
      "connect_timeout": 60000,
      "id": "e6fd8b19-89e5-44e6-8a2a-79e8bf3c31a5",
      "protocol": "http",
      "name": "foo",
      "read_timeout": 60000,
      "port": 80,
      "updated_at": 1612819937,
      "ws_id": "d6020dc4-67f5-4c62-8b45-e2f497c20f5c",
      "retries": 5,
      "write_timeout": 60000
    },
    "route": {               # The Kong route that was matched for this request. Injected only if `include_route_in_opa_input` is set to `true`.
      "id": "bc6d8617-76a7-441f-aa40-32eb1f5be9e6",
      "paths": [
        "\\/"
      ],
      "protocols": [
        "http",
        "https"
      ],
      "strip_path": true,
      "created_at": 1612819949,
      "ws_id": "d6020dc4-67f5-4c62-8b45-e2f497c20f5c",
      "request_buffering": true,
      "updated_at": 1612819949,
      "preserve_host": false,
      "regex_priority": 0,
      "response_buffering": true,
      "https_redirect_status_code": 426,
      "path_handling": "v0",
      "service": {
        "id": "e6fd8b19-89e5-44e6-8a2a-79e8bf3c31a5"
      }
    },
    "consumer": {            # Kong consumer that was used for authentication for this request. Injected only if `include_consumer_in_opa_input` is set to `true`.
      "id": "bc6d8617-76a7-431f-aa40-32eb1f5be7e6",
      "username": "kong-consumer-username"
    }
  }
}

Note that it is possible that Consumer and Service resources are not present for any given request in Kong Gateway.

Expected response from OPA

After OPA is done executing policies, the plugin expects the policy evaluation result in one of the defined formats: boolean or object. Any other format or a status code other than 200 OK results in the plugin returning a 500 Internal Server Error to the client.

Boolean result

OPA can return a true or false result after a policy evaluation. This should suffice for most use cases.

Examples:

To allow the request to be processed further, OPA should send the following response:

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{
  "result": true
}

To deny the request and terminate its processing, OPA should send the following response:

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{
  "result": false
}

Any other fields in the response in this case are ignored.

Object result

In this case, OPA returns an object instead of a boolean result. This allows for injecting custom HTTP headers as well as changing the HTTP status code for rejected requests.

The plugin expects the following structure in the OPA response in this case:

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{
  "result": {
    "allow": <boolean>,
    "status": <HTTP status code>,
    "headers": {
      "<key>": "<value>",
      "<key2>": "<value2>"
    }
  }
}

The only required field in this response is result.allow, which accepts a boolean value.

If result.allow is set to true, then the key-value pairs in result.headers (if any) are injected into the request before it is forwarded to the upstream Service.

If result.allow is set to false, then the key-value pairs in result.headers (if any) are injected into the response and the status code of the response is set to result.status. If result.status is absent then the default 403 status code is sent.