This repo was recently transferred to the Styra organization and work is currently under way to get everything set up here

Open Policy Agent WebAssembly Java SDK (experimental)

This is an SDK for using WebAssembly (wasm) compiled Open Policy Agent policies with Chicory, a pure Java Wasm interpreter.

Initial implementation was based on Open Policy Agent WebAssemby NPM Module and Open Policy Agent Ebassembly dotnet core SDK

Why

We want fast in-process OPA policies evaluations, and avoid network bottlenecks when using opa-java.

Getting Started

Install the module

With Maven add the core module dependency:

<dependency>
    <groupId>com.styra.opa</groupId>
    <artifactId>opa-java-wasm</artifactId>
    <version>latest_release</version>
</dependency>

Usage

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

Import the module

import com.styra.opa.wasm.Opa;

Load the policy

var policy = OpaPolicy.builder().withPolicy(policyWasm).build();

The policyWasm ca be a variety of things, including raw byte array, InputStream, Path, File. The content should be the compiled policy Wasm file, a valid WebAssembly module.

For example:

var policy = OpaPolicy.builder().withPolicy(new File("policy.wasm")).build();

Evaluate the Policy

The OpaPolicy object returned from loadPolicy() has a couple of important APIs for policy evaluation:

data(data) -- Provide an external data document for policy evaluation.

• data MUST be a String, which assumed to be a well-formed stringified JSON

evaluate(input) -- Evaluates the policy using any loaded data and the supplied input document.

• input parameter MUST be a String serialized object, array or primitive literal which assumed to be a well-formed stringified JSON

Example:

input = '{"path": "/", "role": "admin"}';

var policy = OpaPolicy.builder().withPolicy(policyWasm).build();
var result = policy.evaluate(input);
System.out.println("Result is: " + result);

For any opa build created WASM binaries the result set, when defined, will contain a result key with the value of the compiled entrypoint. See https://www.openpolicyagent.org/docs/latest/wasm/ for more details.

Builtins support:

At the moment the following builtins are supported(and, by default, automatically injected when needed):

• Json

  • json.is_valid

• Yaml

  • yaml.is_valid
  • yaml.marshal
  • yaml.unmarshal

Writing the policy

See https://www.openpolicyagent.org/docs/latest/how-do-i-write-policies/

Compiling the policy

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

For example:

opa build -t wasm -e example/allow example.rego

Which is compiling the example.rego policy file with the result set to data.example.allow. The result will be an OPA bundle with the policy.wasm binary included. See ./examples for a more comprehensive example.

See opa build --help for more details.

Development

To develop this library you need to have installed the following tools:

• Java 11+
• Maven
• the opa cli
• tar

the typical command to build and run the tests is:

mvn spotless:apply clean install

to disable the tests based on the Opa testsuite:

OPA_TESTSUITE=disabled mvn spotless:apply install