Secure your Sinatra App by Validating Incoming Twilio Requests

November 28, 2016
Written by
Twilion
Reviewed by
Contributor
Opinions expressed by Twilio contributors are their own
Twilion

secure-sinatra-app
In this guide we will cover how to secure your Sinatra application by validating that incoming requests to your Twilio webhooks are, in fact, from Twilio. With a few lines of code we will write a custom validation for our Sinatra app that uses the Twilio Ruby SDK validator utility. We can then use that validator on our Sinatra app which accept Twilio webhooks to confirm that incoming requests genuinely originated from Twilio. Let’s get started!

This is a migrated tutorial. You can find the original code at https://github.com/TwilioDevEd/api-snippets/blob/master/guides/request-validation-sinatra/

A starting point

If you need help with the setup of a development environment for ruby check the setup documentation.

We will start building from a basic code example implementing a Sinatra application.

Running the example code like:

$ ruby index.rb

This application returns TwiML to any request to "/" without any validation whatsoever:

$ curl -XPOST http://localhost:4567
<?xml version="1.0" encoding="UTF-8"?> <Response><Message>Hello World</Message></Response>
# You can find your Twilio Auth Token here: https://www.twilio.com/console
# Set at runtime as follows:
# $ TWILIO_AUTH_TOKEN="XXXXXXXXXXXXXXXXXXX" ruby index.rb
#
# This will not work unless you export the TWILIO_AUTH_TOKEN environment
# variable.

require 'sinatra'
require 'twilio-ruby'

post '/' do
  content_type 'text/xml'

  response = Twilio::TwiML::MessagingResponse.new
  response.message('Hello World')

  response
end

Adding request validation

To add request validation to your Sinatra App, you'll need an Authentication Token.

We will need an Authentication Token for the Twilio API from the Twilio Console, and this token will be set by exporting a new environment variable:

$ export TWILIO_AUTH_TOKEN=" TWILIO_AUTH_TOKEN_HERE "

To enable request validation through the Rack middleware, we have to add the following line:

use Rack::TwilioWebhookAuthentication, ENV['TWILIO_AUTH_TOKEN'], '/'
# You can find your Twilio Auth Token here: https://www.twilio.com/console
# Set at runtime as follows:
# $ TWILIO_AUTH_TOKEN="XXXXXXXXXXXXXXXXXXX" ruby index.rb
#
# This will not work unless you export the TWILIO_AUTH_TOKEN environment
# variable.

require 'sinatra'
require 'twilio-ruby'
require 'rack'

# To set up environmental variables, see http://twil.io/secure
use Rack::TwilioWebhookAuthentication, ENV['TWILIO_AUTH_TOKEN'], '/'

post '/' do
  content_type 'text/xml'

  response = Twilio::TwiML::MessagingResponse.new
  response.message(body: 'Store Location: 123 Easy St.')

  response
end

Overview and testing

At this point the example has grown and has enabled secure authentication of Twilio requests using your Authentication Token.

We can test that request validation is working by repeating the previous curl step:

$ curl -XPOST http://localhost:4567
Twilio Request Validation Failed.

Confirm that incoming requests to your Sinatra application are genuine with this custom validation logic. It will return <?xml version="1.0" encoding="UTF-8"?> <Response><Message>Hello World</Message></Response> if the request is valid, or Twilio Request Validation Failed. if it is not. Our logic then either continues processing the request or returns error 403 HTTP response for invalid requests attempt.

Validation during testing

If you write tests for your Sinatra application, those tests may fail for routes where you use Twilio request validation. To fix this problem we recommend to use a mocking library in your tests. Take a look at the official Rack documentation for mocking requests and mocking responses.

What’s next?

Validating requests to your Twilio webhooks is a great first step for securing your Twilio application. We recommend reading over our full security documentation for more advice on protecting your app, and the Anti-Fraud Developer’s Guide in particular.

To learn more about securing your Sinatra application in general, check out the security considerations page in the official Sinatra documentation, or you can also take a look at the official Rack documentation and the Twilio Ruby SDK.