Ruby と Rails で Webhook 署名を検証する

require "openssl"

module IkiformSignature
  class Invalid < StandardError; end

  TOLERANCE = 5 * 60

  def self.verify!(body, headers, secret, now: Time.now.to_i)
    id = headers["webhook-id"].to_s
    timestamp = headers["webhook-timestamp"].to_s
    signatures = headers["webhook-signature"].to_s
    raise Invalid, "missing_headers" if id.empty? || timestamp.empty? || signatures.empty?
    raise Invalid, "invalid_timestamp" unless timestamp.match?(/\A[0-9]{1,12}\z/)

    age = now - timestamp.to_i
    raise Invalid, "timestamp_too_old" if age > TOLERANCE
    raise Invalid, "timestamp_too_new" if age < -TOLERANCE

    key = secret.delete_prefix("whsec_").unpack1("m0")
    expected = [OpenSSL::HMAC.digest("SHA256", key, "#{id}.#{timestamp}.#{body}")].pack("m0")
    matched = signatures.split(" ").any? do |entry|
      version, value = entry.split(",", 2)
      version == "v1" && !value.nil? && OpenSSL.secure_compare(value, expected)
    end
    raise Invalid, "no_matching_signature" unless matched
  end
end

require "json"
require "sinatra"
require_relative "ikiform_signature"

SECRET = ENV.fetch("IKIFORM_WEBHOOK_SECRET")

post "/webhooks/ikiform" do
  body = request.body.read
  headers = {
    "webhook-id" => request.env["HTTP_WEBHOOK_ID"],
    "webhook-timestamp" => request.env["HTTP_WEBHOOK_TIMESTAMP"],
    "webhook-signature" => request.env["HTTP_WEBHOOK_SIGNATURE"]
  }

  begin
    IkiformSignature.verify!(body, headers, SECRET)
  rescue IkiformSignature::Invalid => error
    halt 400, error.message
  end

  event = JSON.parse(body)
  logger.info("submission #{event["id"]}") if event["type"] == "submission.created"
  status 204
end

require "json"
require "minitest/autorun"
require_relative "ikiform_signature"

class IkiformSignatureTest < Minitest::Test
  SECRET = "whsec_Fg8c6hm1Gt41v5RSPKm72LggDx8S1mlWkbBYpHPAnpw="
  ROLLED = "whsec_4YWiO+F83kohh/SGNr2zcgChkpVJ65ySVeV23Qabr2A="
  BODY = '{"id":"dlv_01k7v2d4n8r2p6s0w3y5b7c9e1","type":"endpoint.test","timestamp":"2026-10-17T12:00:00.000Z","api_version":"2026-10-17","data":{"endpoint_id":"whk_01k7v2e1b3d5f7h9k1m3n5q7s9","message":"This is a test event from Ikiform."}}'
  HEADERS = {
    "webhook-id" => "dlv_01k7v2d4n8r2p6s0w3y5b7c9e1",
    "webhook-timestamp" => "1792300000",
    "webhook-signature" => "v1,Duq+Iuh0xbRZyS+C/TO5W1hcGLGwg+ifBiWiYkq15qA="
  }.freeze
  NOW = 1_792_300_000 + 30

  def test_accepts_the_vector
    assert_nil IkiformSignature.verify!(BODY, HEADERS, SECRET, now: NOW)
  end

  def test_accepts_either_secret_during_a_roll
    both = HEADERS.merge("webhook-signature" => "#{HEADERS["webhook-signature"]} v1,gfHP3s7ANdIpnM7gewtWtSvTrHgmsbEFgCaeRRR0Eak=")
    assert_nil IkiformSignature.verify!(BODY, both, SECRET, now: NOW)
    assert_nil IkiformSignature.verify!(BODY, both, ROLLED, now: NOW)
  end

  def test_rejects_a_reserialized_body
    pretty = JSON.pretty_generate(JSON.parse(BODY))
    error = assert_raises(IkiformSignature::Invalid) { IkiformSignature.verify!(pretty, HEADERS, SECRET, now: NOW) }
    assert_equal "no_matching_signature", error.message
  end

  def test_rejects_a_stale_timestamp
    error = assert_raises(IkiformSignature::Invalid) { IkiformSignature.verify!(BODY, HEADERS, SECRET, now: NOW + 600) }
    assert_equal "timestamp_too_old", error.message
  end
end

class IkiformWebhooksController < ActionController::API
  def create
    webhook = StandardWebhooks::Webhook.new(Rails.application.credentials.dig(:ikiform, :webhook_secret))
    event = webhook.verify(request.raw_post, {
      "webhook-id" => request.headers["webhook-id"],
      "webhook-timestamp" => request.headers["webhook-timestamp"],
      "webhook-signature" => request.headers["webhook-signature"]
    })

    if event["type"] == "submission.created"
      IkiformSubmissionJob.perform_later(event["id"], event.dig("data", "fields"))
    end
    head :no_content
  rescue StandardWebhooks::WebhookVerificationError => error
    render plain: error.message, status: :bad_request
  end
end

Rails.application.routes.draw do
  post "webhooks/ikiform", to: "ikiform_webhooks#create"
end

class CreateWebhookDeliveries < ActiveRecord::Migration[8.0]
  def change
    create_table :webhook_deliveries do |t|
      t.string :delivery_id, null: false
      t.timestamps
    end
    add_index :webhook_deliveries, :delivery_id, unique: true
  end
end

class IkiformSubmissionJob < ApplicationJob
  queue_as :default

  def perform(delivery_id, fields)
    WebhookDelivery.transaction do
      WebhookDelivery.create!(delivery_id: delivery_id)
      SubmissionMailer.with(fields: fields).notify_team.deliver_now
    end
  rescue ActiveRecord::RecordNotUnique
    Rails.logger.info("Skipping repeated delivery #{delivery_id}")
  end
end