1 files changed, 61 insertions, 0 deletions
diff --git a/app/controllers/action_mailbox/ingresses/mailgun/inbound_emails_controller.rb b/app/controllers/action_mailbox/ingresses/mailgun/inbound_emails_controller.rb
new file mode 100644
index 0000000000..4d194a3e00
--- /dev/null
+++ b/app/controllers/action_mailbox/ingresses/mailgun/inbound_emails_controller.rb
@@ -0,0 +1,61 @@
+class ActionMailbox::Ingresses::Mailgun::InboundEmailsController < ActionMailbox::BaseController
+  before_action :ensure_authenticated
+
+  def create
+    ActionMailbox::InboundEmail.create_and_extract_message_id! raw_email
+    head :ok
+  end
+
+  private
+    def raw_email
+      StringIO.new params.require("body-mime")
+    end
+
+
+    def ensure_authenticated
+      head :unauthorized unless authenticated?
+    end
+
+    def authenticated?
+      Authenticator.new(authentication_params).authenticated?
+    rescue ArgumentError
+      false
+    end
+
+    def authentication_params
+      params.permit(:timestamp, :token, :signature).to_h.symbolize_keys
+    end
+
+
+    class Authenticator
+      cattr_accessor :key
+
+      attr_reader :timestamp, :token, :signature
+
+      def initialize(timestamp:, token:, signature:)
+        @timestamp, @token, @signature = timestamp, token, signature
+      end
+
+      def authenticated?
+        signed? && recent?
+      end
+
+      private
+        def signed?
+          ActiveSupport::SecurityUtils.secure_compare signature, expected_signature
+        end
+
+        # Allow for 10 minutes of drift between Mailgun time and local server time.
+        def recent?
+          time >= 10.minutes.ago
+        end
+
+        def expected_signature
+          OpenSSL::HMAC.hexdigest OpenSSL::Digest::SHA256.new, key, "#{timestamp}#{token}"
+        end
+
+        def time
+          Time.at Integer(timestamp)
+        end
+    end
+end