Logentries.com HMAC Authenticator in Ruby, for Rails

logentries_auth.rb

# Check authenticity of a logentries.com webhook
# cf: https://logentries.com/doc/webhookalert/
# cf: https://blog.logentries.com/2013/02/webhooks-are-hmac-authenticated/
require 'openssl'
require 'base64'
require 'digest/md5'

class LogentriesAuth
  attr_reader :request

  def initialize(request)
    @request = request
  end

  def authorized?
    auth_sig == signature   &&
      auth_user == user     &&
      30.seconds.ago < date &&
      !nonce_replay?
  end

  private

  def canonical
    [
      request.method,
      request.headers['Content-Type'],
      Base64.encode64(Digest::MD5.digest(request.body.string)),
      request.headers['Date'],
      request.path,
      nonce,
    ].map(&:strip).join("\n")
  end

  def signature
    dg = OpenSSL::Digest.new('sha1')
    Base64.encode64( OpenSSL::HMAC.digest(dg, secret, canonical)).strip
  end

  def date
    DateTime.parse(request.headers['Date'])
  end

  def auth_sig
    request.headers['Authorization'].split(':').last
  end

  def auth_user
    request.headers['Authorization'].split(':').first.split.last
  end

  def user
    ENV.fetch('LOGENTRIES_WEBHOOK_KEY', ':').split(':').first
  end

  def secret
    ENV.fetch('LOGENTRIES_WEBHOOK_KEY', ':').split(':').last
  end

  def nonce
    request.headers['X-Le-Nonce']
  end

  def nonce_replay?
    return true if Redis.current.get("logentries::#{nonce}").present?
    Redis.current.set("logentries::#{nonce}", 1, ex: 7.days)
    false
  end
end
=begin
The MIT License (MIT)
Copyright (c) 2016 PacerPro, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
=end