login_form.haml

- form_tag '/login' do
  .flash= flash[:notice]
  %p
    = label_tag :username
    = text_field_tag :username, :value => params[:username]
  %p
    = label_tag :password
    = text_field_tag :password, :value => params[:password]
  %p
    = submit_tag "Login"

some_test.rb

describe "Some Controller Test" do
  it "allow a logged in user" do
    fred = Factory(:user)
    # I want to authenticate fred as a logged in user here
    get '/dashboard'
    last_response.should.be.ok
  end

  it "reject a non-logged in user" do
    get '/dashboard'
    last_response.should.redirect_to '/login'
  end
end

warden_config.rb

  configure do
    use Rack::Session::Cookie
    use Warden::Manager do |manager|
      manager.default_strategies :password
      manager.failure_app = WardenHandler
    end
    use Rack::Flash
  end

  Warden::Manager.serialize_into_session{ |user| user.nil? ? nil : user.id }
  Warden::Manager.serialize_from_session{ |id|   id.nil? ? nil : User.find(id) }

  Warden::Strategies.add(:password) do
    def valid?
      params['username'] || params['password']
    end

    def authenticate!
      u = User.authenticate(params['username'], params['password'])
      u.nil? ? fail!("Could not log in") : success!(u)
    end
  end

warden_handler.rb

class WardenHandler < Sinatra::Application
  every '/unauthenticated/?' do
    flash[:notice] = "That username and password are not correct!"
    status 401
    haml_template 'warden/new'
  end

  get '/login/?' do
    haml_template 'warden/new'
  end

  post '/login/?' do
    env['warden'].authenticate!
    redirect "/"
  end

  get '/logout/?' do
    warden_handler.logout
    redirect '/login'
  end
end