Usage

Rails 3

Gemfile

gem 'devise_webmoney'
gem "rack-webmoney"

adding wmid column:

rails g migration add_wmid_to_user

and add this:

def self.up
  add_column :users, :wmid, :string, :limit => 12

  add_index :users, :wmid, :unique => true
end

def self.down
  remove_column :users, :wmid
end

application.rb

...
config.middleware.insert_before(Warden::Manager, Rack::Webmoney,
  :credentials => { :site_holder_wmid => 'your_site_wmid',
                    :app_rids => { 'localhost'   => 'xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx',
                                   'example.com' => 'xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx' }},
  :mode => Rails.env)
...

config/initializers/devise.rb

config.webmoney_auto_register = true

user.rb

devise :webmoney_authenticatable

Your authentication form should return params == ‘webmoney’ form Webmoney authentication process begin.