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Castle Webhooks

TL;DR

To integrate Castle webhooks with ngrok:

  1. Launch your local webhook. npm start
  2. Launch ngrok. ngrok http 3000
  3. Configure Castle webhooks with your ngrok URL.
  4. Secure your webhook requests with verification.

This guide covers how to use ngrok to integrate your localhost app with Castle by using Webhooks. Castle webhooks can be used to notify an external application whenever specific events occur in your Castle account.

By integrating ngrok with Castle, you can:

  • Develop and test Castle webhooks locally, eliminating the time in deploying your development code to a public environment and setting it up in HTTPS.
  • Inspect and troubleshoot requests from Castle in real-time via the inspection UI and API.
  • Modify and Replay Castle Webhook requests with a single click and without spending time reproducing events manually in your Castle account.
  • Secure your app with Castle validation provided by ngrok. Invalid requests are blocked by ngrok before reaching your app.

Step 1: Start your app​

For this tutorial, we'll use the sample NodeJS app available on GitHub.

To install this sample, run the following commands in a terminal:

git clone https://github.com/ngrok/ngrok-webhook-nodejs-sample.git
cd ngrok-webhook-nodejs-sample
npm install

This will get the project installed locally.

Now you can launch the app by running the following command:

npm start

The app runs by default on port 3000.

You can validate that the app is up and running by visiting http://localhost:3000. The application logs request headers and body in the terminal and responds with a message in the browser.

Step 2: Launch ngrok​

Once your app is running successfully on localhost, let's get it on the internet securely using ngrok!

  1. If you're not an ngrok user yet, just sign up for ngrok for free.

  2. Download the ngrok agent.

  3. Go to the ngrok dashboard and copy your Authtoken.
    Tip: The ngrok agent uses the auth token to log into your account when you start a tunnel.

  4. Start ngrok by running the following command:

    ngrok http 3000

  5. ngrok will display a URL where your localhost application is exposed to the internet (copy this URL for use with Castle). ngrok agent running

Step 3: Integrate Castle​

To register a webhook on your Castle account follow the instructions below:

  1. Access the Castle dashboard and sign in using your Castle account.

  2. On the left menu, click the gear icon close to your name and then click Configuration.

  3. On the Application page, click Webhooks on the top menu, and then click Add a new Endpoint.

  4. On the Set up a new webhook endpoint page, enter the URL provided by the ngrok agent to expose your application to the internet in the ENDPOINT URL field (i.e. https://1a2b-3c4d-5e6f-7g8h-9i0j.sa.ngrok.io). Castle ENDPOINT URL

  5. Select all events under the EVENTS TO SUBSCRIBE section and then click Save.

  6. On the Webhooks page, click the slider icon to activate the webhook.

Run Webhooks with Castle and ngrok​

Castle sends different request body contents depending on the event that is being triggered. You can trigger new calls from Castle to your application by following the instructions below.

  1. On the Application page, click Webhooks on the top menu and then click Test for your webhook.

  2. On the Test the webhook endpoint popup, select an event in the EVENT field and then click Send test webhook. Note: Optionally, you can create an event by using the Castle SDK.

    Confirm your localhost app receives the test event notification and logs both headers and body in the terminal.

Inspecting requests​

When you launch the ngrok agent on your local machine, you can see two links:

  • The URL to your app (it ends with ngrok-free.app for free accounts or ngrok.app for paid accounts when not using custom domains)
  • A local URL for the Web Interface (a.k.a Request Inspector).

The Request Inspector shows all the requests made through your ngrok tunnel to your localhost app. When you click on a request, you can see details of both the request and the response.

Seeing requests is an excellent way of validating the data sent to and retrieved by your app via the ngrok tunnel. That alone can save you some time dissecting and logging HTTP request and response headers, methods, bodies, and response codes within your app just to confirm you are getting what you expect.

To inspect Castle's webhooks call, launch the ngrok web interface (i.e. http://127.0.0.1:4040), and then click one of the requests sent by Castle.

From the results, review the response body, header, and other details:

ngrok Request Inspector

Replaying requests​

The ngrok Request Inspector provides a replay function that you can use to test your code without the need to trigger new events from Castle. To replay a request:

  1. In the ngrok inspection interface (i.e. http://localhost:4040), select a request from Castle.

  2. Click Replay to execute the same request to your application or select Replay with modifications to modify the content of the original request before sending the request.

  3. If you choose to Replay with modifications, you can modify any content from the original request. For example, you can modify the id field inside the body of the request.

  4. Click Replay.

Verify that your local application receives the request and logs the corresponding information to the terminal.

Secure webhook requests​

The ngrok signature webhook verification feature allows ngrok to assert that requests from your Castle webhook are the only traffic allowed to make calls to your localhost app.

Note: This ngrok feature is limited to 500 validations per month on free ngrok accounts. For unlimited, upgrade to Pro or Enterprise.

This is a quick step to add extra protection to your application.

  1. Access the Castle dashboard and sign in using your Castle account.

  2. On the left menu, click the gear icon close to your name and then click Configuration.

  3. On the Application page, copy the value of the API SECRET field.

  4. Restart your ngrok agent by running the command, replacing {your api secret} with the value you have copied before:

    ngrok http 3000 --verify-webhook castle --verify-webhook-secret {your api secret}

  5. Access the Castle dashboard and test the webhook endpoint or create an event by using the Castle SDK.

Verify that your local application receives the request and logs information to the terminal.