Use the Heroku Platform API to find an app by config variable (namely `MANDRILL_USERNAME`)

heroku_scan.rb

require 'httparty'
require 'pry'

ADDRESS = "[email protected]"

class Heroku
  include HTTParty
  base_uri "https://api.heroku.com"

  def self.get_token
    return ENV["HEROKU_AUTH_TOKEN"] if ENV["HEROKU_AUTH_TOKEN"]
    print "Your auth token > "
    gets.chomp
  end

  default_options[:headers] = {
    "Content-Type" => "application/json",
    "Accept" => "application/vnd.heroku+json; version=3",
    "Authorization" => "Bearer #{get_token}"
  }

  def apps
    self.class.get "/apps"
  end

  def config_vars app_id
    self.class.get "/apps/#{app_id}/config-vars"
  end
end

c   = Heroku.new
app = c.apps.find do |a|
  puts a["name"]
  vars = c.config_vars a["name"]
  vars["MANDRILL_USERNAME"] == ADDRESS
end
puts "Offending app is: #{app}"

binding.pry