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devise.rb

module ActionDispatch::Routing
  class Mapper
    def authenticate(scope = Devise.default_scope)
      constraint = lambda do |request|
        request.env["warden"].authenticate!(:scope => scope)
      end

      constraints(constraint) do
        yield
      end
    end
  end
end

routes.rb

authenticate do
  resource :profile
end

authenticate(:admin) do
  namespace :admin do
    match "/dashboard", :to => "dashboard#index", :as => :dashboard
  end
end