Writing a Webhook

Responses

Your Webhook must handle the RESTful request described above and send back an appropriate status code. Your Webhook must send back to FusionAuth an HTTP response code that indicates whether or not the event was successfully handled or not. If your Webhook handled the event properly, it must send back an HTTP response status code of 2xx. If there was any type of error or failure, your Webhook must send back a non 2xx HTTP response status.

Configuration

Once your Webhook is complete and listening for events, you must configure your Webhook URL in FusionAuth. To add a webhook navigate to Settings → Webhooks. If you have multiple Webhooks configured for a single Application, the transaction setting for the event or the User Action will dictate if FusionAuth will commit the transaction or not.

Calling FusionAuth APIs In Webhooks

Some events fire on creation of an entity in FusionAuth, such as user.create. You may want to modify the created entity, but if your webhook tries to modify the newly created object in a webhook handling the create event, the operation will fail. This is due to the fact that the operation occurs in a transaction and has not yet completed when the webhook runs.

In fact, the created user will not be visible to any other API request until the transaction is committed. The operation fails because the webhook is trying to modify an object that has not yet been completely created and has not yet been committed to persistant storage. Depending upon your transaction configuration for a particular event, FusionAuth may wait until all webhooks have responded before committing the transaction.

Even if you configure your webhook transaction to not require any webhooks to succeed, it is unlikely your code will operate as intended due to the parallel timing of the requests. The user.create event was not designed to allow a webhook to retrieve and modify the user.

Here’s a scenario:

• You have a webhook that catches the user.create event.

• It extracts the user’s email address.

• Then it queries a non FusionAuth database and adds a custom user.data.premiumUser field to the FusionAuth user object based on the query results.

• At user login, the value of the user.data.premiumUser field will be placed into a JWT for other applications to access.

In this example, you have a few options; which one is best depends on when you need to be able to read from the user.data.premiumUser field.

• Provide the custom data field at user creation, instead of updating the user via a webhook. This option is the simplest, but may not be possible if users are self registering. In this case, the field is available from the moment the user is created.

• Review available events and determine if a subsequent event occurs in your workflow. For example, user.registration.create may occur after a user is created. At this point, the user will exist and can be modified. If an event happens repeatedly, make the modification idempotent. In this case, the field is available as soon as the other event fires.

• Don’t process the data in the webhook. Instead, push the event JSON to a queue and return success. Have a queue consumer pull the data off and update the user.data.premiumUser field. The consumer can retry multiple times if the user object has not yet been fully created, which can happen if there are other webhooks whose completion is required. In this case, the field is available when the consumer finishes.

While this scenario is most obvious when a user or registration is being created, it applies to all webhooks. The final state of the operation which caused the webhook is not persisted to FusionAuth until after the webhook finishes.

Example Code

Here’s a simple example of a Webhook written in Node using Express. In this example, if the event is a user.delete event, this code deletes all of the user’s Todos.

In this example we are also checking the HTTP Authorization header for an API key. Using an API key or some type of authentication helps secure your Webhook to prevent malicious requests. You can configure the API key via the FusionAuth Web Interface or the API using the Headers of the Webhook configuration.

router.route('/fusionauth-webhook').post((req, res) => {
  const authorization = req.header('Authorization');
  if (authorization !== 'API-KEY') {
    res.status(401).send({
      'errors': [{
        'code': '[notAuthorized]'
      }]
    });
    return;
  }

  const request = req.body;
  if (request.event.type === 'user.delete') {
    todo.deleteAll(request.event.user.id)
      .then(() => {
        res.sendStatus(200);
      })
      .catch(function(err) {
        _handleDatabaseError(res, err);
      });
  }
});