Setup basic auth as a middleware for a rack application.

lockdown.rb

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

  def call(env)
    request = Rack::Request.new(env)

    if request.path != '/'
      auth = Rack::Auth::Basic::Request.new(env)

      return unauthorized unless auth.provided?
      return bad_request unless auth.basic?

      if auth.credentials == [username, password]
        env['REMOTE_USER'] = auth.username
        return @app.call(env)
      end

      unauthorized
    else
      @app.call(env)
    end
  end

  private
  def username
    'username'
  end
  
  def password
    'password'
  end
  
  def unauthorized(www_authenticate = challenge)
    return [ 401,
      { 'Content-Type' => 'text/plain',
        'Content-Length' => '0',
        'WWW-Authenticate' => www_authenticate.to_s },
      []
    ]
  end

  def bad_request
    return [ 400,
      { 'Content-Type' => 'text/plain',
        'Content-Length' => '0' },
      []
    ]
  end

  def challenge
    'Basic realm="%s"' % realm
  end

  def realm
    'Realm'
  end
end