Added README.md

Author: tgeens

README.md

@@ -0,0 +1,102 @@
+# opa-async-java-client
+![build](https://github.com/content-cloud/opa-java-client/workflows/build/badge.svg?branch=main)
+
+An asynchronous java client library for the [OpenPolicyAgent](https://www.openpolicyagent.org/) [REST API](https://www.openpolicyagent.org/docs/latest/rest-api/).
+
+
+This repository has two components:
+
+* `opa-async-java-client` is the actual client for the OPA [REST API](https://www.openpolicyagent.org/docs/latest/rest-api/)
+* `rego-java` a library that models the Open Policy Agent policy language [Rego](https://www.openpolicyagent.org/docs/how-do-i-write-policies.html)
+
+
+The design of the project is borrowed from [Bisnode/opa-java-client](https://github.com/Bisnode/opa-java-client), but
+uses an async programming model instead, which makes it suitable to be used in a reactive application stack.
+
+This client library uses the JDK11+ HttpClient by default, but allows you to plug in your own http-client by providing
+an implementation for the [OpaRestClient](https://github.com/xenit-eu/opa-async-java-client/blob/main/opa-async-java-client/src/main/java/eu/xenit/contentcloud/abac/opa/client/rest/OpaRestClient.java)
+interface. 
+
+## Installation
+
+**Prerequisites:** Java 11 or higher
+
+Using Gradle:
+
+```groovy
+implementation "eu.xenit.contentcloud.abac:opa-async-java-client:${version}"
+```
+
+Using Maven:
+
+```xml
+<dependency>
+    <groupId>eu.xenit.contentcloud.abac</groupId>
+    <artifactId>opa-async-java-client</artifactId>
+    <version>${version}</version>
+</dependency>
+```
+
+## Usage
+
+Create an `OpaClient` instance:
+
+```
+OpaClient client = OpaClient.builder()
+    .url("http://localhost:8181")
+    .build();
+```
+
+### Policies
+
+#### List the ids of all policies:
+```
+client.listPolicies().thenAccept(response -> {
+    var policies = response.getResult();
+    policies.forEach(policy -> log.info("policy id: {}", policy.getId()));
+});
+```
+
+#### Get a policy:
+```
+client.getPolicy("my-policy-id").thenAccept(response -> {
+    AbstractSyntaxTree ast = response.getResult().getAst();
+    // do something with the `ast`
+});
+```
+
+#### Create a policy
+```
+client.upsertPolicy("policy_id", "content of the policy").join();
+```
+
+### Data API
+### Query API
+### Compile API
+
+### Error handling
+
+Error handling is not yet properly supported.
+
+When the HTTP status code is 400 or higher, the returned
+`CompletableFuture<T>` will fail, with `HttpStatusException` as inner exception cause.
+
+Example:
+
+```
+var result = client.upsertPolicy("my-policy", "invalid policy");
+
+result.handle((response, ex) -> {
+    if (ex != null) {
+        if (ex.getCause() instanceof HttpStatusException) {
+            if (((HttpStatusException) ex.getCause()).getStatusCode() == 400) {
+                throw new IllegalArgumentException("policy content is not valid");
+            }
+        }
+        throw RuntimeException(ex);
+    }
+
+    // happy path
+    return response;
+});
+```

gradle.properties

@@ -1,4 +1,4 @@
-group=eu.contentcloud.opa
+group=eu.xenit.contentcloud.abac
 
 lombokVersion=1.18.16
 slf4jVersion =1.7.30