Aim for Rails 3.0.0.beta1 compatibility. A few issues are still pending with Warden.

Gemfile

@@ -1,6 +1,7 @@
 source "http://gemcutter.org"
 
-gem "rails", "3.0.0.beta"
+# Need to install Rails from source
+gem "rails", "3.0.0.beta1"
 gem "warden", "0.9.4"
 gem "sqlite3-ruby", :require => "sqlite3"
 gem "webrat", "0.7"

lib/devise.rb

@@ -1,3 +1,5 @@
+require 'active_support/core_ext/numeric/time'
+
 module Devise
   autoload :FailureApp, 'devise/failure_app'
   autoload :Schema, 'devise/schema'

lib/devise/failure_app.rb

@@ -56,7 +56,7 @@ module Devise
     # yet, but we still need to store the uri based on scope, so different scopes
     # would never use the same uri to redirect.
     def store_location!(scope)
-      session[:"#{scope}.return_to"] = request.request_uri if request && request.get?
+      session[:"#{scope}.return_to"] = request.fullpath if request && request.get?
     end
   end
 end

lib/devise/rails.rb

@@ -5,8 +5,16 @@ module Devise
   class Engine < ::Rails::Engine
     engine_name :devise
 
-    config.middleware.use Warden::Manager do |config|
-      Devise.configure_warden(config)
+    initializer "devise.add_middleware" do |app|
+      app.config.middleware.use Warden::Manager do |config|
+        Devise.configure_warden(config)
+      end
+    end
+
+    initializer "devise.add_url_helpers" do |app|
+      if app.routes.respond_to?(:url_helpers)
+        Devise::FailureApp.send :include, app.routes.url_helpers
+      end
     end
   end
 end

test/controllers/helpers_test.rb

@@ -23,6 +23,10 @@ class MockController < ApplicationController
     "http"
   end
 
+  def script_name
+    ""
+  end
+
   def symbolized_path_parameters
     {}
   end