StripeEvent

StripeEvent is built on the ActiveSupport::Notifications API. Incoming webhook requests are authenticated by retrieving the event object from Stripe. Define subscribers to handle specific event types. Subscribers can be a block or an object that responds to #call.

Install

# Gemfile
gem 'stripe_event'

# config/routes.rb
mount StripeEvent::Engine, at: '/my-chosen-path' # provide a custom path

Usage

# config/initializers/stripe.rb
Stripe.api_key = ENV['STRIPE_SECRET_KEY'] # e.g. sk_live_1234

StripeEvent.configure do |events|
  events.subscribe 'charge.failed' do |event|
    # Define subscriber behavior based on the event object
    event.class       #=> Stripe::Event
    event.type        #=> "charge.failed"
    event.data.object #=> #<Stripe::Charge:0x3fcb34c115f8>
  end

  events.all do |event|
    # Handle all event types - logging, etc.
  end
end

Subscriber objects that respond to #call

class CustomerCreated
  def call(event)
    # Event handling
  end
end

class BillingEventLogger
  def initialize(logger)
    @logger = logger
  end

  def call(event)
    @logger.info "BILLING:#{event.type}:#{event.id}"
  end
end

StripeEvent.configure do |events|
  events.all BillingEventLogger.new(Rails.logger)
  events.subscribe 'customer.created', CustomerCreated.new
end

Subscribing to a namespace of event types

StripeEvent.subscribe 'customer.card.' do |event|
  # Will be triggered for any customer.card.* events
end

Securing your webhook endpoint

StripeEvent automatically fetches events from Stripe to ensure they haven't been forged. However, that doesn't prevent an attacker who knows your endpoint name and an event's ID from forcing your server to process a legitimate event twice. If that event triggers some useful action, like generating a license key or enabling a delinquent account, you could end up giving something the attacker is supposed to pay for away for free.

To prevent this, StripeEvent supports using HTTP Basic authentication on your webhook endpoint. If only Stripe knows the basic authentication password, this ensures that the request really comes from Stripe. Here's what you do:

Arrange for a secret key to be available in your application's environment variables or secrets.yml file. You can generate a suitable secret with the rake secret command. (Remember, the secrets.yml file shouldn't contain production secrets directly; it should use ERB to include them.)

Configure StripeEvent to require that secret be used as a basic authentication password, using code along the lines of these examples:

# STRIPE_WEBHOOK_SECRET environment variable
StripeEvent.authentication_secret = ENV['STRIPE_WEBHOOK_SECRET']
# stripe_webhook_secret key in secrets.yml file
StripeEvent.authentication_secret = Rails.application.secrets.stripe_webhook_secret

When you specify your webhook's URL in Stripe's settings, include the secret as a password in the URL, along with any username:
```
 https://stripe:my-secret-key@myapplication.com/my-webhook-path
```

This is only truly secure if your webhook endpoint is accessed over SSL, which Stripe strongly recommends anyway.

Configuration

If you have built an application that has multiple Stripe accounts--say, each of your customers has their own--you may want to define your own way of retrieving events from Stripe (e.g. perhaps you want to use the user_id parameter from the top level to detect the customer for the event, then grab their specific API key). You can do this:

StripeEvent.event_retriever = lambda do |params|
  api_key = Account.find_by!(stripe_user_id: params[:user_id]).api_key
  Stripe::Event.retrieve(params[:id], api_key)
end

class EventRetriever
  def call(params)
    api_key = retrieve_api_key(params[:user_id])
    Stripe::Event.retrieve(params[:id], api_key)
  end

  def retrieve_api_key(stripe_user_id)
    Account.find_by!(stripe_user_id: stripe_user_id).api_key
  rescue ActiveRecord::RecordNotFound
    # whoops something went wrong - error handling
  end
end

StripeEvent.event_retriever = EventRetriever.new

If you'd like to ignore particular webhook events (perhaps to ignore test webhooks in production, or to ignore webhooks for a non-paying customer), you can do so by returning nil in you custom event_retriever. For example:

StripeEvent.event_retriever = lambda do |params|
  return nil if Rails.env.production? && !params[:livemode]
  Stripe::Event.retrieve(params[:id])
end

StripeEvent.event_retriever = lambda do |params|
  account = Account.find_by!(stripe_user_id: params[:user_id])
  return nil if account.delinquent?
  Stripe::Event.retrieve(params[:id], account.api_key)
end

Without Rails

StripeEvent can be used outside of Rails applications as well. Here is a basic Sinatra implementation:

require 'json'
require 'sinatra'
require 'stripe_event'

Stripe.api_key = ENV['STRIPE_SECRET_KEY']

StripeEvent.subscribe 'charge.failed' do |event|
  # Look ma, no Rails!
end

post '/_billing_events' do
  data = JSON.parse(request.body.read, symbolize_names: true)
  StripeEvent.instrument(data)
  200
end

Testing

Handling webhooks is a critical piece of modern billing systems. Verifying the behavior of StripeEvent subscribers can be done fairly easily by stubbing out the HTTP request used to authenticate the webhook request. Tools like Webmock and VCR work well. RequestBin is great for collecting the payloads. For exploratory phases of development, UltraHook and other tools can forward webhook requests directly to localhost. You can check out test-hooks, an example Rails application to see how to test StripeEvent subscribers with RSpec request specs and Webmock. A quick look:

# spec/requests/billing_events_spec.rb
require 'spec_helper'

describe "Billing Events" do
  def stub_event(fixture_id, status = 200)
    stub_request(:get, "https://api.stripe.com/v1/events/#{fixture_id}").
      to_return(status: status, body: File.read("spec/support/fixtures/#{fixture_id}.json"))
  end

  describe "customer.created" do
    before do
      stub_event 'evt_customer_created'
    end

    it "is successful" do
      post '/_billing_events', id: 'evt_customer_created'
      expect(response.code).to eq "200"
      # Additional expectations...
    end
  end
end

Note: 'Test Webhooks' Button on Stripe Dashboard

This button sends an example event to your webhook urls, including an id of evt_00000000000000. To confirm that Stripe sent the webhook, StripeEvent attempts to retrieve the event details from Stripe using the given id. In this case the event does not exist and StripeEvent responds with 401 Unauthorized. Instead of using the 'Test Webhooks' button, trigger webhooks by using the Stripe API or Dashboard to create test payments, customers, etc.

keithwoody/stripe_event