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# frozen_string_literal: true
module ActionMailbox
# Ingests inbound emails from Mailgun. Requires the following parameters:
#
# - +body-mime+: The full RFC 822 message
# - +timestamp+: The current time according to Mailgun as the number of seconds passed since the UNIX epoch
# - +token+: A randomly-generated, 50-character string
# - +signature+: A hexadecimal HMAC-SHA256 of the timestamp concatenated with the token, generated using the Mailgun API key
#
# Authenticates requests by validating their signatures.
#
# Returns:
#
# - <tt>204 No Content</tt> if an inbound email is successfully recorded and enqueued for routing to the appropriate mailbox
# - <tt>401 Unauthorized</tt> if the request's signature could not be validated, or if its timestamp is more than 2 minutes old
# - <tt>404 Not Found</tt> if Action Mailbox is not configured to accept inbound emails from Mailgun
# - <tt>422 Unprocessable Entity</tt> if the request is missing required parameters
# - <tt>500 Server Error</tt> if the Mailgun API key is missing, or one of the Active Record database,
# the Active Storage service, or the Active Job backend is misconfigured or unavailable
#
# == Usage
#
# 1. Give Action Mailbox your {Mailgun API key}[https://help.mailgun.com/hc/en-us/articles/203380100-Where-can-I-find-my-API-key-and-SMTP-credentials-]
# so it can authenticate requests to the Mailgun ingress.
#
# Use <tt>rails credentials:edit</tt> to add your API key to your application's encrypted credentials under
# +action_mailbox.mailgun_api_key+, where Action Mailbox will automatically find it:
#
# action_mailbox:
# mailgun_api_key: ...
#
# Alternatively, provide your API key in the +MAILGUN_INGRESS_API_KEY+ environment variable.
#
# 2. Tell Action Mailbox to accept emails from Mailgun:
#
# # config/environments/production.rb
# config.action_mailbox.ingress = :mailgun
#
# 3. {Configure Mailgun}[https://documentation.mailgun.com/en/latest/user_manual.html#receiving-forwarding-and-storing-messages]
# to forward inbound emails to +/rails/action_mailbox/mailgun/inbound_emails/mime+.
#
# If your application lived at <tt>https://example.com</tt>, you would specify the fully-qualified URL
# <tt>https://example.com/rails/action_mailbox/mailgun/inbound_emails/mime</tt>.
class Ingresses::Mailgun::InboundEmailsController < ActionMailbox::BaseController
before_action :authenticate
def create
ActionMailbox::InboundEmail.create_and_extract_message_id! params.require("body-mime")
end
private
def authenticate
head :unauthorized unless authenticated?
end
def authenticated?
if key.present?
Authenticator.new(
key: key,
timestamp: params.require(:timestamp),
token: params.require(:token),
signature: params.require(:signature)
).authenticated?
else
raise ArgumentError, <<~MESSAGE.squish
Missing required Mailgun API key. Set action_mailbox.mailgun_api_key in your application's
encrypted credentials or provide the MAILGUN_INGRESS_API_KEY environment variable.
MESSAGE
end
end
def key
Rails.application.credentials.dig(:action_mailbox, :mailgun_api_key) || ENV["MAILGUN_INGRESS_API_KEY"]
end
class Authenticator
attr_reader :key, :timestamp, :token, :signature
def initialize(key:, timestamp:, token:, signature:)
@key, @timestamp, @token, @signature = key, Integer(timestamp), token, signature
end
def authenticated?
signed? && recent?
end
private
def signed?
ActiveSupport::SecurityUtils.secure_compare signature, expected_signature
end
# Allow for 2 minutes of drift between Mailgun time and local server time.
def recent?
Time.at(timestamp) >= 2.minutes.ago
end
def expected_signature
OpenSSL::HMAC.hexdigest OpenSSL::Digest::SHA256.new, key, "#{timestamp}#{token}"
end
end
end
end
|
