adding a blocklist break-glass header for Rack::Attack

When blocklisting broad IP ranges using the Rails Rack::Attack gem, it can be valuable to have a break-glass HTTP header so that legitimate users in a blocked range can still access the webapp.

The Rack::Attack docs provide most of the information on how to do this, however the syntax in the current example does not match the format of a header injected into the browser using an extension such as SimpleModifyHeaders.

As it turns out, any such headers are uppercased and prefixed with HTTP_. So if in your browser extension you set your header as SuperSecretKey, Rack::Attack would pass it through as HTTP_SUPERSECRETKEY.

The below code snippet illustrates, and also dumps out all headers to the console as a comma delimited list.

class Rack::Attack

  p "~~~~~~~~ RAAAACK ATTAAAAAAAACK ~~~~~~~~"

  # safelist by HTTP header
  Rack::Attack.whitelist("mark any authenticated user as safe") do |request|

    p "~~ HEADER CHECK ~~"

    p request.env.sort.compact.reject(&:empty?).join(',')

    puts request.env.key?("HTTP_SUPERSECRETKEY")
    puts request.env["HTTP_SUPERSECRETKEY"]
    request.env["HTTP_SUPERSECRETKEY"] == "Hunter2"