api.rb

require 'sinatra'
require 'json'
require 'securerandom'

helpers do
  def protected!
    return if authorized?
    headers['WWW-Authenticate'] = 'Basic realm="Restricted Area"'
    halt 401, "Not authorized"
  end

  def authorized?
    @auth ||=  Rack::Auth::Basic::Request.new(request.env)
    @auth.provided? and @auth.basic? and @auth.credentials and @auth.credentials == ['billing', 'gateway']
  end
end

get '/' do
  'Hello'
end

get '/validate' do
  protected!

  send(%i(response_ok response_fail response_503 response_timeout).sample)
end

def response_ok
  content_type :json

  JSON.dump(
    id: SecureRandom.hex(8),
    paid: true,
    failure_message: nil
  )
end

def response_fail
  content_type :json

  JSON.dump(
    id: SecureRandom.hex(8),
    paid: false,
    failure_message: 'insufficient_funds'
  )
end

def response_503
  halt 503, 'Service Unavailable'
end

def response_timeout
  sleep 15
  halt 503, 'Service Unavailable'
end