[Twilio] Validate Signature of Request (in pure Ruby)

twilio.rb

require 'base64'
require 'openssl'

# See: https://www.twilio.com/docs/usage/security#validating-requests
#
# Example of AWS API Gateway (HTTP) + Lambda
def is_twilio_request_valid?(event)
  # Create a string that is your URL with the full query string
  url = "https://#{event['headers']['host']}#{event['rawPath']}"
  # Sort the list of POST variables by the parameter name
  body = event['body']
  body = Base64.decode64(body) if event['isBase64Encoded']
  h = URI.decode_www_form(body).to_h
  a = h.keys.sort.map { |k| "#{k}#{h[k]}" }
  # Append each POST variable, name and value, to the string with no delimiters
  str = "#{url}#{a.join}"
  # Hash the resulting string using HMAC-SHA1, using your AuthToken Primary as the key
  key = ENV['TWILIO_AUTHTOKEN_PRIMARY']
  sig = Base64.strict_encode64(OpenSSL::HMAC.digest('sha1', key, str))
  event['headers']['x-twilio-signature'] == sig
end