chore(examples): Show dynamic feature flags with LaunchDarkly

examples/nodejs-express-launchdarkly/.env.local.example

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+# NODE_ENV is not set by the environment
+ARCJET_ENV=development
+# Add your Arcjet key from https://app.arcjet.com
+ARCJET_KEY=
+# Add your LaunchDarkly SDK key. Click on the project name in this list
+# to be taken to the SDK keys: https://app.launchdarkly.com/settings/projects
+LAUNCHDARKLY_SDK_KEY=

examples/nodejs-express-launchdarkly/README.md

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+<a href="https://arcjet.com" target="_arcjet-home">
+  <picture>
+    <source media="(prefers-color-scheme: dark)" srcset="https://arcjet.com/logo/arcjet-dark-lockup-voyage-horizontal.svg">
+    <img src="https://arcjet.com/logo/arcjet-light-lockup-voyage-horizontal.svg" alt="Arcjet Logo" height="128" width="auto">
+  </picture>
+</a>
+
+# Arcjet Dynamic Configuration via LaunchDarkly Feature Flags
+
+This example shows how to dynamically configure Arcjet via
+[LaunchDarkly](https://launchdarkly.com) feature flags. It is implemented with a Node.js
+[Express](https://expressjs.com/) server, but the theory can apply to any environment.
+
+## How to use
+
+1. From the root of the project, install the SDK dependencies.
+
+   ```bash
+   npm ci
+   ```
+
+2. Enter this directory and install the example's dependencies.
+
+   ```bash
+   cd examples/nodejs-express-launchdarkly
+   npm ci
+   ```
+
+3. Rename `.env.local.example` to `.env.local` and add your [Arcjet key](https://app.arcjet.com)
+and LaunchDarkly SDK key ([click on the project name in this list to be taken to the SDK
+keys](https://app.launchdarkly.com/settings/projects)).
+
+4. Create four flags in LaunchDarkly with the following settings:
+   - Shield Mode:
+      - Name: `shieldMode`
+      - Key: `shieldMode`
+      - Configuration: **Custom**
+      - Is this flag temporary? No
+      - Flag Type: String
+      - Variations
+         1. Name: `LIVE`, value: `LIVE`
+         2. Name: `DRY_RUN`, value: `DRY_RUN`
+      - Default Variations
+         * Serve when targeting is ON: `LIVE`
+         * Serve when targeting is OFF: `DRY_RUN`
+   - Sliding Window Mode:
+      - Name: `slidingWindowMode`
+      - Key: `slidingWindowMode`
+      - Configuration: **Custom**
+      - Is this flag temporary? No
+      - Flag Type: String
+      - Variations
+         1. Name: `LIVE`, value: `LIVE`
+         2. Name: `DRY_RUN`, value: `DRY_RUN`
+      - Default Variations
+         * Serve when targeting is ON: `LIVE`
+         * Serve when targeting is OFF: `DRY_RUN`
+   - Sliding Window Max:
+      - Name: `slidingWindowMax`
+      - Key: `slidingWindowMax`
+      - Configuration: **Custom**
+      - Is this flag temporary? No
+      - Flag Type: Number
+      - Variations
+         1. Name: `Regular`, value: `100`
+         2. Name: `Clamped Down`, value: `2`
+      - Default Variations
+         * Serve when targeting is ON: `Regular`
+         * Serve when targeting is OFF: `Clamped Down`
+   - Sliding Window Interval:
+      - Name: `slidingWindowInterval`
+      - Key: `slidingWindowInterval`
+      - Configuration: **Custom**
+      - Is this flag temporary? No
+      - Flag Type: Number
+      - Variations
+         1. Name: `Regular`, value: `60`
+         2. Name: `Clamped Down`, value: `10`
+      - Default Variations
+         * Serve when targeting is ON: `Regular`
+         * Serve when targeting is OFF: `Clamped Down`
+
+5. Start the server.
+
+   ```bash
+   npm start
+   ```
+
+   This assumes you're using Node.js 20 or later because the `start` script
+   loads a local environment file with `--env-file`. If you're using an older
+   version of Node.js, you can use a package like
+   [dotenv](https://www.npmjs.com/package/dotenv) to load the environment file.
+
+6. Visit `http://localhost:3000/`.
+
+7. Refresh the page about 5-10 times. The rate-limit should not be hit.
+
+8. Go to the "Contexts" section in the LaunchDarkly dashboard and click on "guest".
+
+9. Change the `slidingWindowMax` and `slidingWindowInterval` to `Clamped Down`,
+click "Review and save", then "Save changes" in the modeal that appears.
+
+10. Refresh your web application and note the new configuration is announced in
+the terminal. Refresh another few times to see the rate-limit take effect.

examples/nodejs-express-launchdarkly/index.js

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+import arcjet from "./lib/arcjet.js";
+import express from "express";
+
+const app = express();
+app.get("/", async (req, res) => {
+  // Get an instance of Arcjet from our custom module
+  const aj = await arcjet();
+
+  // Get a decision from Arcjet for the incoming request
+  const decision = await aj.protect(req);
+
+  // If the decision is denied, return an appropriate status code
+  if (decision.isDenied()) {
+    if (decision.reason.isRateLimit()) {
+      return res.status(429).send("Too many requests");
+    } else {
+      return res.status(403).send("Forbidden");
+    }
+  }
+
+  // If the decision is allowed, return a successful response
+  res.send("Hello World!");
+});
+
+app.listen(3000, () => {
+  console.log("Server started on port 3000");
+});

examples/nodejs-express-launchdarkly/lib/arcjet.js

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+import _arcjet, { shield, slidingWindow } from "@arcjet/node";
+import { getArcjetConfig } from "./launchdarkly.js";
+
+// Initialize Arcjet with your site key and rules
+const aj = _arcjet({
+  // Get your site key from https://app.arcjet.com
+  // and set it as an environment variable rather than hard coding.
+  // See: https://www.npmjs.com/package/dotenv
+  key: process.env.ARCJET_KEY,
+  rules: [],
+});
+
+// This function will return an Arcjet instance with the latest rules
+const arcjet = async () => {
+  // Get the latest configuration from LaunchDarkly
+  const newConfig = await getArcjetConfig();
+
+  // Return the Arcjet instance with the latest rules
+  return aj.withRule(shield({ mode: currentConfig.shieldMode })).withRule(
+    slidingWindow({
+      mode: currentConfig.slidingWindowMode,
+      max: currentConfig.slidingWindowMax,
+      interval: currentConfig.slidingWindowInterval,
+    })
+  );
+};
+
+export default arcjet;

examples/nodejs-express-launchdarkly/lib/launchdarkly.js

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+import * as ld from "@launchdarkly/node-server-sdk";
+
+// Initialize LaunchDarkly client
+const client = ld.init(process.env.LAUNCHDARKLY_SDK_KEY);
+
+export const getArcjetConfig = async () => {
+  // Wait for the LaunchDarkly client to be initialized
+  await client.waitForInitialization({ timeout: 500 });
+
+  // Set the user context for LaunchDarkly - in this example, every user is treated the same.
+  const context = { key: "guest" };
+
+  // Get the latest configuration from LaunchDarkly
+  const shieldMode = await client.variation("shieldMode", context, "LIVE");
+  const slidingWindowMode = await client.variation(
+    "slidingWindowMode",
+    context,
+    "LIVE"
+  );
+  const slidingWindowMax = await client.variation(
+    "slidingWindowMax",
+    context,
+    60
+  );
+  const slidingWindowInterval = await client.variation(
+    "slidingWindowInterval",
+    context,
+    60
+  );
+
+  return {
+    shieldMode,
+    slidingWindowMode,
+    slidingWindowMax,
+    slidingWindowInterval,
+  };
+};