intercom_webhooks.rb

## Running this file locally
# Save this file to intercom_webhooks.rb
# In the same directory as the file type "gem install sinatra" and "gem install json" into your command line.
# Install Ngrok (Webhook testing software) blogpost on using it here: https://www.intercom.com/blog/how-to-get-up-and-running-with-messenger-apps-using-ngrok/
# In your command line type "ruby intercom_webhook.rb"
# Once ngrok is installed you can type "ngrok http 4567" in your command line to start Ngrok.
# Now create a new webhook in your developer hub (app.intercom.com/developers/_/webhooks) pointing to the URL that Ngrok gives you
# Save the webhook once you have selected the topic you want notifications for
# Trigger the action to send the webhook notification. For example closing a conversation


require 'sinatra'
require 'json'

WH_SECRET = "<YOUR-SECRET-HERE>" # If you don't have a secret remove this line
APP_URL_REGEX = /\/apps\/(?<app_id>\w+)/

# Authenticate requests
def check_signature(payload_body)
  wh_signature = request.env['HTTP_X_HUB_SIGNATURE']
  puts "Received signature: #{wh_signature}"

  if wh_signature.nil? || wh_signature.empty?
    puts "No signature received with the webhook."
  else
    computed_signature = 'sha1=' + OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new('sha1'), WH_SECRET, payload_body).to_s
    puts "Calculated signature: #{computed_signature}"
    puts "Signatures match: #{wh_signature === computed_signature}"

    return halt 401, "Invalid signature!" if !(wh_signature === computed_signature)
  end
end

def parse_details(url)
  match = url.match(APP_URL_REGEX)
  {
    app_id: match[:app_id]
  }
end

post '/' do
  # First getting the payload as simple string, we need it to compute the signature
  payload_body = request.body.read

  # Check the signature
  check_signature(payload_body)

  # Parsing the payload to JSON to be able to get the values
  payload = JSON.parse(payload_body)

  wh_topic = payload["topic"]
  wh_data = payload["data"]
  links = wh_data["item"]["links"]
  conversation_id = wh_data["item"]["id"]
  puts "Topic: #{wh_topic}"
  puts "Data: #{wh_data.to_json}"
  puts "Payload: #{payload}"
  puts ""
end