What is a very simple authentication scheme for Sinatra/Rack

I am busy porting a very small web app from ASP.NET MVC 2 to Ruby/Sinatra.

In the MVC app, FormsAuthentication.SetAuthCookie was being used to set a persistent cookie when the users login was validated correctly against the database.

I was wondering what the equivalent of Forms Authentication would be in Sinatra? All the authentication frameworks seem very bulky and not really what I'm looking for.

Solution

Here is a very simple authentication scheme for Sinatra.

I’ll explain how it works below.

class App < Sinatra::Base
  set :sessions => true

  register do
    def auth (type)
      condition do
        redirect "/login" unless send("is_#{type}?")
      end
    end
  end

  helpers do
    def is_user?
      @user != nil
    end
  end

  before do
    @user = User.get(session[:user_id])
  end

  get "/" do
    "Hello, anonymous."
  end

  get "/protected", :auth => :user do
    "Hello, #{@user.name}."
  end

  post "/login" do
    session[:user_id] = User.authenticate(params).id
  end

  get "/logout" do
    session[:user_id] = nil
  end
end

For any route you want to protect, add the :auth => :user condition to it, as in the /protected example above. That will call the auth method, which adds a condition to the route via condition.

The condition calls the is_user? method, which has been defined as a helper. The method should return true or false depending on whether the session contains a valid account id. (Calling helpers dynamically like this makes it simple to add other types of users with different privileges.)

Finally, the before handler sets up a @user instance variable for every request for things like displaying the user’s name at the top of each page. You can also use the is_user? helper in your views to determine if the user is logged in.