gem install sinatra-any

require 'sinatra'
require 'sinatra/any'

any "/api/v2/*" do
  halt 403 if unauthorized?
end

get "/api/v2/widgets" do
  do_somthing_for_authorized_users
end

@jbarnette (John Barnette) for convicing me this is a real problem
to solve because Rails can't follow specs.