*.rb

# Add this your environment.rb or environment/*.rb file

config.middleware.use(::Rack::Middleware::BasicAuth,
  :username => "myuser",
  :password => "my$uperpa$$vvord",
  :domain   => "mydomain.com"
)

basic_auth.rb

module Rack
  module Middleware
    class BasicAuth
      def initialize(app, options = {})
        @app = app
        @options = options
      end

      def call(env, options = {})
        unless env['REMOTE_USER']
          auth = Rack::Auth::Basic::Request.new(env)

          return unauthorized! unless auth.provided?
          return bad_request! unless auth.basic?
          return unauthorized! unless authorize(*auth.credentials)

          env['REMOTE_USER'] = auth.username
        end

        @app.call(env)
      end

      def authorize(username, password)
        @options[:username] == username && @options[:password] == password
      end

      def unauthorized!
        [ 401, {'WWW-Authenticate' => %(Basic realm="#{@options[:domain]}")}, 'Authorization Required' ]
      end

      def bad_request!
        [ 400, 'Bad Request' ]
      end
    end
  end
end