Quack, quack, quack. Use duck typing instead of hardcoding everything, closes #1281.

CHANGELOG.rdoc

@@ -1,3 +1,6 @@
+* enhancements
+  * Use serialize_into_session and serialize_from_session in Warden serialize to improve extensibility
+
 * bug fix
   * Properly deprecate setup_mail
   * Fix encoding issues with email regexp

lib/devise/models/authenticatable.rb

@@ -82,6 +82,15 @@ module Devise
       module ClassMethods
         Devise::Models.config(self, :authentication_keys, :request_keys, :strip_whitespace_keys, :case_insensitive_keys, :http_authenticatable, :params_authenticatable)
 
+        def serialize_into_session(record)
+          [record.to_key, record.authenticatable_salt]
+        end
+
+        def serialize_from_session(key, salt)
+          record = to_adapter.get(key)
+          record if record && record.authenticatable_salt == salt
+        end
+
         def params_authenticatable?(strategy)
           params_authenticatable.is_a?(Array) ?
             params_authenticatable.include?(strategy) : params_authenticatable

lib/devise/rails/warden_compat.rb

@@ -15,21 +15,16 @@ end
 
 class Warden::SessionSerializer
   def serialize(record)
-    [record.class.name, record.to_key, record.authenticatable_salt]
+    klass = record.class
+    array = klass.serialize_into_session(record)
+    array.unshift(klass.name)
   end
 
   def deserialize(keys)
-    if keys.size == 2
-      raise "Devise changed how it stores objects in session. If you are seeing this message, " <<
-        "you can fix it by changing one character in your secret_token or cleaning up your " <<
-        "database sessions if you are using a db store."
-    end
-
-    klass, id, salt = keys
+    klass, *args = keys
 
     begin
-      record = ActiveSupport::Inflector.constantize(klass).to_adapter.get(id)
-      record if record && record.authenticatable_salt == salt
+      ActiveSupport::Inflector.constantize(klass).serialize_from_session(*args)
     rescue NameError => e
       if e.message =~ /uninitialized constant/
         Rails.logger.debug "[Devise] Trying to deserialize invalid class #{klass}"