Writing a Webhook

Writing a Webhook

In order to appropriately handle requests from the FusionAuth event, you must build a simple HTTP Webhook that listens for requests from the FusionAuth event system. Your Webhook must be designed to receive simple HTTP POST requests with a JSON request body. The HTTP request will be sent using a Content-Type header value of application/json.

Additional headers may be added to the request by adding headers to the Webhook configuration.

• Writing a Webhook

• Responses

• Configuration

  • Application Scoped Events

  • Tenant Scoped Events

  • Example Configuration After 1.37.0

  • Example Configuration Before 1.37.0

• Retries

  • Retry Examples

• Calling FusionAuth APIs In Webhooks

• Example Code

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.

Then, configure the Tenant to listen for the event by navigating to Tenants → Your Tenant → Webhooks.

If you have multiple Webhooks configured for a single Tenant, the transaction setting for the event will dictate if FusionAuth will commit the transaction or not.

As of version 1.37.0 if you have multiple webhooks assigned to different tenants but configured for the same event, such as user.create, only the events matching both tenant and type will be delivered. For example, imagine you have Pied Piper and Hooli tenants and both have different webhooks (piedpier.com/webhook and hooli.com/webhook) and each is configured to listen only to their tenant for the user.create webhook event. In this case, piedpiper.com/webhook would receive only Pied Piper user creation event information; likewise hooli.com/webhook will receive only webhooks for the user.create event from the Hooli tenant.

Prior to version 1.37.0 if you have multiple tenants listening for the same event, they will all receive that event and can filter on the provided tenantId to determine if they should handle the event.

Retries

If the webhook transaction succeeds, FusionAuth will try to send the payload to any failed webhooks again. For example, if there are three webhooks set up to listen to a user.update request, and the transaction level is set to "Any single webhook must succeed" and one webhook succeeds, the two failures will be retried. FusionAuth will retry sending the payload up to three additional times. This retry logic means that webhook endpoints may receive a payload multiple times and should be prepared to handle such a situation.

If not enough of the webhooks succeed to satisfy the transaction type initially, the operation will not succeed; for example, the user will not be updated. The originating call will receive an error HTTP status code.

If a webhook endpoint times out, this is considered a failure, the same as if a non 2xx status code is returned. If the endpoint does not respond after the retries, the failure will be logged in the system log.

Retry Examples

Below are flow diagrams of example requests. The order of the requests is not guaranteed, but is merely illustrative. In each of these, an API call such as a user update is made, and FusionAuth has been configured to fire off to three different webhooks at that time. The webhook transaction level and the webhook success statuses vary.

Here’s a situation with three webhooks and a webhook transaction level of "No webhooks are required to succeed". In this scenario, FusionAuth "fires and forgets":

Next, consider the scenario with three webhooks and a webhook transaction configuration of "Any single webhook must succeed" where "Webhook 1" succeeds. In this case, the other two webhooks are retried up to three additional times. "Webhook 2" succeeds eventually, but "Webhook 3" fails:

Here’s a configuration with three webhooks and a webhook transaction configuration of "Any single webhook must succeed" where all webhooks fail or time out. In this case, there are no retries, since the webhook transaction level was not met.

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 database 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 persistent 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);
      });
  }
});