rack builder

config.ru

require 'rack'
require 'rack/auth/basic'

class HelloWorld
  def call(env)
    [200, {"Content-Type" => "text/html"}, "Hello World!"]
  end
end

class WorldHello
  def call(env)
    [200, {"Content-Type" => "text/html"}, "World Hello!"]
  end
end

class Guard
  def initialize(app)
    @app = app
  end

  def call(env)
    if env['PATH_INFO'] =~ Regexp.new('^/api')
      GRACK.call(env)
    else
      @app.call(env)
    end
  end
end

GRACK = Rack::Builder.new do
  use Rack::Auth::Basic do |username, password|
    true
  end

  run WorldHello.new
end

BUILDER = Rack::Builder.new do
  use Guard

  run HelloWorld.new
end

# try http://localhost:3000 => response "HelloWorld"
# try http://localhost:3000/api => challenge and response "WorldHello"
run BUILDER