inspect the rack env before it hits the rails app

application.rb

#config/application.rb

config.middleware.use "Peekaboo"

peekaboo.rb

#put this in lib/peekaboo.rb
class Peekaboo
  def initialize(app)
    @app = app
  end

  def call(env)
    puts env.inspect
    #here's where it hits the rails app, you could change anything in env before it
    status, headers, response = @app.call(env)
    [status, headers, response]
  end
end