Never ever do this in a Rack middleware, memory leak + security issue included

gistfile1.rb

class MyMiddleWare
    REDIRECT = [302, { 'Content-Type' => 'text/html; charset=utf-8', 'Location' => '/admin' }, []]

    def initialize(app)
      @app = app
    end

    def call(env)
      if <blabla>
        REDIRECT
      else
        @app.call(env)
      end
    end
end

Because the constant will be later modified, cookie will be appended over and over and so will session_id. This will grant all visitors all cookies, make session theft very easy, pass session from one guy to the other and all sort of nasty things.

Never use constant as Rack response NEVER, or make sure they are deep frozen.