path_based_auth.rb

class PathBasedAuth
  def initialize(app, opts, &block)
    @app = app
    @path = opts[:path]
    @block = block
    @auth = Rack::Auth::Basic.new(app, &block)
  end

  def call(env)
    if path_matches?(env)
      @auth.call(env)
    else
      @app.call(env)
    end
  end

  private

  def path_matches?(env)
    env['REQUEST_URI'] =~ @path
  end
end