Kubewarden Policy SDK for JavaScript/TypeScript

[!WARNING] The SDK is experimental and under active development.

The official JavaScript/TypeScript SDK for writing Kubewarden policies. This SDK allows you to write Kubernetes admission policies using TypeScript/JavaScript that compile to WebAssembly modules.

Installation

npm install kubewarden-policy-sdk

Quick Start

Basic Policy Structure

import { Validation, writeOutput } from 'kubewarden-policy-sdk';

function validate() {
  // Read the admission request
  const validationRequest = Validation.readValidationRequest();
  const settings = validationRequest.settings;

  // Your policy logic here
  const isValid = yourValidationLogic(validationRequest.request);

  // Create response
  const response = new Validation.ValidationResponse(
    isValid,
    isValid ? undefined : 'Request rejected by policy',
    undefined, // mutated_object (for mutating policies)
    undefined, // warnings
    { customData: 'example' }, // annotations
  );

  // Write the response
  writeOutput(response);
}

// Export the validate function
(globalThis as any).validate = validate;

Using Host Capabilities

[!IMPORTANT]
Logging to stdout will break your policy. Always use console.error() for logging instead of console.log() to avoid policy failures.

The SDK provides access to Kubewarden's host capabilities:

Network Operations

import { hostCapabilities } from 'kubewarden-policy-sdk';

// DNS lookup
const dnsResult = hostCapabilities.Net.lookupHost('example.com');
console.error('IPs:', dnsResult.ips);

OCI Registry Operations

import { hostCapabilities } from 'kubewarden-policy-sdk';

// Get OCI manifest
const manifest = hostCapabilities.OciManifest.getManifest('registry.io/image:tag');
console.error('Manifest:', manifest);

// Verify image signatures
const verificationResult = hostCapabilities.OciSignatureVerifier.verifyPubKeysImage(
  'registry.io/image:tag',
  ['-----BEGIN PUBLIC KEY-----\n...\n-----END PUBLIC KEY-----'],
);

Kubernetes API Access

import { hostCapabilities } from 'kubewarden-policy-sdk';

// Get a Kubernetes resource
const resource = hostCapabilities.Kubernetes.getResource({
  apiVersion: 'v1',
  kind: 'Pod',
  name: 'my-pod',
  namespace: 'default',
});

// List resources
const pods = hostCapabilities.Kubernetes.listResourcesByNamespace({
  apiVersion: 'v1',
  kind: 'Pod',
  namespace: 'default',
});

Cryptographic Operations

import { hostCapabilities } from 'kubewarden-policy-sdk';

// Verify certificate
const cert = hostCapabilities.Crypto.CertificateUtils.fromString(
  '-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----',
  'Pem',
);

const verificationResult = hostCapabilities.Crypto.verifyCert(
  cert,
  [], // certificate chain
  '2025-12-31T23:59:59Z', // not_after
);

Complete Example Policy

import { Validation, writeOutput } from 'kubewarden-policy-sdk';
import type { Pod } from 'kubernetes-types/core/v1';

interface PolicySettings {
  ignoredNamespaces?: string[];
  allowPrivileged?: boolean;
}

function validate() {
  const validationRequest = Validation.readValidationRequest();
  const settings = validationRequest.settings as PolicySettings;
  const pod = validationRequest.request.object as Pod;

  // Skip validation for ignored namespaces
  if (settings.ignoredNamespaces?.includes(pod.metadata?.namespace || '')) {
    writeOutput(new Validation.ValidationResponse(true));
    return;
  }

  // Check for privileged containers
  const hasPrivilegedContainers =
    pod.spec?.containers?.some(container => container.securityContext?.privileged === true) ||
    false;

  if (hasPrivilegedContainers && !settings.allowPrivileged) {
    writeOutput(
      new Validation.ValidationResponse(
        false,
        'Privileged containers are not allowed',
        undefined,
        undefined,
        { violationType: 'privileged-container' },
      ),
    );
    return;
  }

  writeOutput(new Validation.ValidationResponse(true));
}

(globalThis as any).validate = validate;

API Reference

Core Classes

Validation.ValidationResponse

new ValidationResponse(
  accepted: boolean,           // Whether the request is accepted
  message?: string,           // Optional rejection message
  mutated_object?: any,       // For mutating admission controllers
  warnings?: string[],        // Optional warnings
  annotations?: Record<string, string> // Custom annotations
)

Validation.readValidationRequest()

Reads and parses the incoming Kubernetes admission request.

Host Capabilities

Network

• lookupHost(hostname: string): DNS resolution

Container Registry

• getManifest(image: string): Get OCI manifest
• getManifestConfig(image: string): Get manifest configuration
• getManifestDigest(image: string): Get manifest digest

Signature Verifier

• verifyPubKeysImage(image: string, pubKeys: string[]): Verify with public keys
• verifyKeylessExactMatch(image: string, keyless: KeylessInfo[]): Keyless verification
• verifyKeylessPrefix(image: string, keyless: KeylessPrefixInfo[]): Prefix-based keyless verification
• verifyGithubActions(image: string, owner: string): GitHub Actions verification

Kubernetes

• getResource(request: GetResourceRequest): Get a specific resource
• listResourcesByNamespace(request: ListResourcesRequest): List resources in namespace
• listAllResources(request: ListResourcesRequest): List all resources
• canI(request: CanIRequest): Check permissions using the Kubernetes authorization API

Cryptographic

• verifyCert(cert: Certificate, certChain: Certificate[], notAfter?: string): Verify certificates
• CertificateUtils.fromString(certString: string, encoding: CertificateEncoding): Create certificate from string
• CertificateUtils.toString(cert: Certificate): Convert certificate to string

For complete documentation of all available host capabilities, see the Kubewarden Host Capabilities Reference.

Building Policies

Prerequisites

• Node.js and npm
• Javy - JavaScript to WebAssembly compiler
• kwctl - Kubewarden CLI tool

Build Process

1. Install the SDK:

   npm install kubewarden-policy-sdk

2. Write your policy (e.g., main.ts)

3. Set up your project structure with appropriate package.json, tsconfig.json, and webpack.config.js

4. Build the policy:

   make build           # Compile TypeScript and bundle JavaScript
   make annotated-policy.wasm  # Compile to WebAssembly and annotate

5. Test your policy:

   kwctl run annotated-policy.wasm -r request.json

Plugin Location

The Javy plugin required for compilation is included in the package at:

node_modules/kubewarden-policy-sdk/plugin/javy-plugin-kubewarden.wasm

Testing

The SDK includes comprehensive testing utilities. See the demo policy for examples of:

• Unit testing with Jest
• End-to-end testing with BATS
• Mock host capabilities for testing

Examples

The best way to get started is with the JavaScript Policy Template which provides a ready-to-use project structure and examples.

You can also check out the demo policy in this repository for a complete working example that demonstrates:

• Basic admission control logic
• Host capabilities usage
• Configuration handling
• Testing strategies

Contributing

We welcome contributions! Please see the contributing guidelines for more information.

Development Setup

git clone https://github.com/kubewarden/policy-sdk-js.git
cd policy-sdk-js/js
npm install
npm test

License

This project is licensed under the Apache 2.0 License - see the LICENSE file for details.

Support

• Documentation
• Slack (#kubewarden)
• Issues