Best Practices

Handling duplicate events

Your webhook endpoints may occasionally receive the same event more than once. This is due to the nature of network connectivity. We recommend making your event processing idempotent to handle duplicate events. One way of doing this is to log events that you've processed and to skip processing for already-logged events.

Checking Signatures

Requests from Persona will contain a Persona-Signature header with an HMAC. You should check that any request is authentic and safe to process by comparing this value with your own digest, computed from the request body and your webhook secret. Your webhook secret can be found in the Webhooks section of the Dashboard.

The Persona-Signature header contains two comma-separated key-value pairs encoding information about the request. The first key-value pair will be in the form t=<unix_timestamp> and represents the unix time that the request was sent. The second key-value pair will be in the form v1=<signature>, where the signature is computed from your webhook secret and a dot-separated string composed of the unix timestamp joined with the request body.

Sample code for checking signatures:

t, v1 = request.headers['Persona-Signature'].split(',').map { |value| value.split('=').second }
computed_digest = OpenSSL::HMAC.hexdigest('SHA256', <YOUR_WEBHOOK_SECRET>, "#{t}.#{request.body.read}")

if v1 == computed_digest
  # Handle verified webhook event
end

t, v1 = [value.split('=')[1] for value in request.headers['Persona-Signature'].split(',')]
computed_digest = hmac.new(<YOUR_WEBHOOK_SECRET>.encode(), (t + '.' + request.data.decode('utf-8')).encode(), 'sha256').hexdigest()

if hmac.compare_digest(v1, computed_digest):
  # Handle verified webhook event

const sigParams = {}
request.headers['Persona-Signature']
	.split(',')
	.forEach(pair => {
		const [key, value] = pair.split('=');
		sigParams[key] = value;
	})

if (sigParams.t && sigParams.v1) {
	const hmac = crypto.createHmac('sha256', <YOUR_WEBHOOK_SECRET>)
  	.update(`${sigParams.t}.${request.body}`)
  	.digest('hex');
  
	if (crypto.timingSafeEqual(Buffer.from(hmac), Buffer.from(sigParams.v1))) {
		// Handle verified webhook event
	}
}

🚧

Parsing JSON when Computing HMACs

In some languages, parsing the JSON may result in something that's not equivalent to the event body. For example, JavaScript may round floats and reduce precision. We recommend using the raw event body when computing the HMAC.

CSRF protection

If you’re using Rails, Django, or another web framework, your site might automatically check that every POST request contains a CSRF token. This is an important security feature that helps protect you and your users from cross-site request forgery attempts. However, this security measure might also prevent your site from processing legitimate events. If so, you might need to exempt the webhooks route from CSRF protection.

class PersonaController < ApplicationController
  # If your controller accepts requests other than Persona webhooks,
  # you'll probably want to use `protect_from_forgery` to add CSRF
  # protection for your application. But don't forget to exempt
  # your webhook route!
  protect_from_forgery except: :webhook

  def webhook
    # Process webhook data in `params`
  end
end

import json

# Webhooks are always sent as HTTP POST requests, so ensure
# that only POST requests reach your webhook view by
# decorating `webhook()` with `require_POST`.
#
# To ensure that the webhook view can receive webhooks,
# also decorate `webhook()` with `csrf_exempt`.
@require_POST
@csrf_exempt
def webhook(request):
  # Process webhook data in `request.body`