Add EventNotificationHandler

[xavdid-stripe]

Why?

We've been designing a streamlined approach to handling incoming events that is easy to get right and hard to get wrong. This PR has the initial implementation of this new system.

The only other pending item is to add a method to allow handling a webhook without verifying the signature. This is good for testing and for Event Bridge, which doesn't use the signature-based verification. Otherwise, this is ready for review.

What?

• add EventHandler class
• add event handler constructor on StripeClient
• add tests
• tweak linting
• added attr_reader :requestor on Client so we could modify the context live. Don't love it, but it's what it is

Example usage

client = Stripe::StripeClient.new(api_key)
handler = client.notification_handler(webhook_secret) do |notif, client, details|
  puts "Received unhandled notification:", notif.type
end

handler.on_v1_billing_meter_error_report_triggered do |event_notification, client|
  meter = event_notification.fetch_related_object
  puts "Meter #{meter.display_name} (#{meter.id}) had a problem"
end

post "/webhook" do
  webhook_body = request.body.read
  sig_header = request.env["HTTP_STRIPE_SIGNATURE"]

  begin
    handler.handle(webhook_body, sig_header)
    status 200
  rescue Stripe::SignatureVerificationError => e
    puts "Signature verification failed:", e.message
    status 400
  end
end

See Also

• DEVSDK-2822
• ⚠️ Add strongly typed EventNotifications #1650

[xavdid-stripe]

@prathmesh-stripe this is ready for final review!