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1.1.0 • Public • Published

Work in Progress -- Contributions welcome!!

Open Policy Agent WebAssemby NPM Module

This is the source for the @open-policy-agent/opa-wasm NPM module which is a small SDK for using WebAssembly (wasm) compiled Open Policy Agent Rego policies.

Getting Started

Install the module

npm install @open-policy-agent/opa-wasm 


There are only a couple of steps required to start evaluating the policy.

Import the module and initialize a Rego object

const Rego = require("@open-policy-agent/opa-wasm")
rego = new Rego()

Load the policy


The load_policy request returns a Promise with the loaded policy. Typically this means loading it in an async function like:

const policy = await rego.load_policy(policy_wasm)

Or something like:

rego.load_policy(policy_wasm).then(policy => {
    // evaluate or save the policy
}, error => {
    console.error("Failed to load policy: " + error)

The policy_wasm needs to be either the raw byte array of the compiled policy wasm file, or a web assembly module.

For example:

const fs = require('fs');
const policy_wasm = fs.readFileSync('policy.wasm')

Alternatively the bytes can be pulled in remotely from a fetch or in some cases (like CloudFlare Workers) the wasm is loaded directly into the javascript context through external APIs.

Evaluate the Policy

The loaded policy object returned from load_policy() has, as of now, only one method for evaluating the policy: eval_bool(). This will evaluate the policy and expects a boolean query result. The return value is a javascript Boolean.

The input parameter must be a JSON string.


input = '{"path": "/", "role": "admin"}';
rego.load_policy(policy_wasm).then(policy => {
    allowed = policy.eval_bool(input);
    console.log("allowed = " + allowed);
}).catch( error => {
    console.error("Failed to load policy: " + error);

Writing the policy


Compiling the policy

Either use the Compile REST API or opa build CLI tool.

For example:

opa build -d example.rego 'data.example.allow = true'

Which is compiling the example.rego policy file with the query data.example.allow = true. See ./examples for a more comprehensive example.

See opa build --help for more details.


npm i @open-policy-agent/opa-wasm

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