Implementing Webhooks

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Overview

Usually, when an application wants to consume information from another it makes a request to obtain such information.

Webhooks turn this around: the producer of information calls the consumer when data is available. This way, the consumer doesn’t have to poll the producer regularly to obtain information.

Metriport will call your app’s webhook endpoint when user data is available - there’s no way for your application to request data exposed through webhooks.

To enable this integration approach with Metriport:

1. Expose a public endpoint on your app;
2. Set this endpoint URL on the Developers page in the developer dashboard, or via the Update Settings endpoint;
3. This will generate a webhook key that should be used to authenticate requests on your app’s endpoint (webhook) - see authentication and generating a new webhook key below.

General requirements for the endpoint:

1. Public endpoint accessible from the internet;
2. Does not do an HTTP redirect (redirects will not be followed);
3. Accepts a POST HTTP request;
4. Verifies requests using the HTTP header x-metriport-signature - see authentication below;
5. Responds 200 in under 4 seconds - we recommend processing the webhook request asynchronously;
6. Accepts and responds to a ping message;
7. Be idempotent - it should accept being called more than once with the same payload, with no changes to the end result.

Additionally, your endpoint will need to accept and process different messages when they become available - specifically:

1. Patient data messages.

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Authentication

When Metriport sends a webhook message, it includes an x-metriport-signature header - this is an HMAC SHA-256 hash computed using your webhook key and the body of the webhook message.

At a high level, an HMAC works by taking a secret key (webhook key from the Settings page) and a message, and performing iterative hashes of the two to create a signature. That signature is compared against the signature in the header for equality. If the signatures are equal, you can trust the webhook payload is authentic and has not been tampered with. If they aren’t equal, you should throw it away.

You can use this header to verify that the webhook messages sent to your endpoint are from Metriport.

Avoid parsing the request body before generating the signature - it could result in a slightly different signature that’s enough to invalidate it.

Here’s an example of how you can do this in Node.js - see the full sample code here:

const metriportApi = new MetriportMedicalApi(apiKey, { sandbox: true });

function verifySignature(req: Request): boolean {
  const signature = String(req.headers["x-metriport-signature"]);
  const payload = req.body; // unparsed, raw body
  if (metriportApi.verifyWebhookSignature(webhookKey, payload, signature)) {
    console.log(`Signature verified`);
    return true;
  } else {
    console.log(`Signature verification failed`);
    return false;
  }
}

The important thing is to make sure you use a trusted cryptography library in whatever language you choose to validate the webhook message in.

You can also validate the HMAC in Python - see the full sample code here:

import hmac
import hashlib
import json

def verify_webhook_signature(key: str, body: str, signature: str) -> bool:
    """
    Verify the HMAC signature for a given message and key.

    :param key: your webhook key (string).
    :param body: the raw body of the webhook request (string).
    :param signature: the signature obtained from the webhook request header (string).
    :return: True if signature is verified, False otherwise.
    """

    key_bytes = key.encode('utf-8')
    body_bytes = body.encode('utf-8')

    hmac_obj = hmac.new(key_bytes, body_bytes, hashlib.sha256)
    computed_signature = hmac_obj.hexdigest()
    if hmac.compare_digest(computed_signature, signature):
        print('Signature verified')
        return True
    else:
        print('Signature verification failed')
        return False

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Generating a new webhook key

If using the dashboard: simply delete your webhook URL on the Developers page, save, and enter it again.

If using the API: set the webhook URL to an empty string via the Update Settings endpoint, and then set it to your desired URL making another request to the same endpoint.

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Format

Webhook requests contain the relevant information on the body of the HTTP request.

There are several types of messages you can expect to receive:

• ping: validation of the webhook connection between Metriport and your app;
• Medical API messages.

In general, upon successful receiving of these messages, it’s expected that your app responds with a 200 HTTP status code (OK).

There’s no need to include anything on the response body.

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The ping message

This is a simple message to validate access to your app’s webhook endpoint. Your app should accept a POST request with this body…

{
  "ping": "<random-sequence>"
  "meta": {
    "messageId": "<message-id>",
    "when": "<date-time-in-utc>",
    "type": "ping"
  }
}

…and respond to this request by sending back the <random-sequence> as below:

{
  "pong": "<random-sequence>"
}

You can check the webhook mock server available on our repository for a simple implementation of this message.

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Medical API messages

When using the Medical API, Metriport will send Webhook messages containing status updates to your app, as soon as the data becomes available.

You can see Webhook details specific to the Medical API, including which operations trigger Webhook messages, on this page.

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Meta data

Webhook updates will contain meta information.

Example payload:

{
  "meta": {
    "messageId": "<message-id>",
    "when": "<date-time-in-utc>",
    "type": "medical.medical.consolidated-data"
  },
  ...
}

The format follows:

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Retries

Sometimes, due to temporary network disruption (or whatever other reason), a Webhook payload may fail to be delivered to your app. In these cases, Metriport will store the failed requests, and you can then manually retry them - using either the dashboard, or the API.

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Retry Using the Dashboard

On the Developers page in the dashboard, you’re able to see the count of Webhook requests currently processing, and a count of outstanding ones that failed:

To retry failed requests, simply click the Retry button, and those requests will be sent to your app again.

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Retry Using the API

1. Using the Get Webhook Status endpoint, check to see if there are any failed requests;
2. Then, use the Retry Webhook requests endpoint, to kick off the retry.