Only Rails 3 is supported.

Uses fbgraph (http://github.com/nsanta/fbgraph)
Could use the Oauth2 gem directly, but it is more than likely that you
would want to use other features of facebook (ie post feed updates).


How to use
----------
Setup devise (http://github.com/plataformatec/devise), use Rails 3

Include the gem in Gemfile after devise:
  gem 'devise'
  gem 'devise_oauth2_facebook'

Include the ':devise_oauth2_facebook' in your model:

  devise :database_authenticatable, :registerable, :confirmable,
         :recoverable, :rememberable, :trackable, :validatable, :devise_oauth2_facebook


Add the following config options:

$ config/initializers/devise.rb

  config.facebook_api_key = "KEY"
  config.facebook_api_secret = "SECRET"
  config.facebook_permissions = 'offline_access,email,publish_stream'

Good minimum to have is "offline_access,email"

Create a migration file to add the columns:

  add_column :users, :facebook_uid, :string
  add_column :users, :facebook_token, :string

Finally, update your view to include "Login with facebook" link:
  <%= link_to "Login with facebook", user_fb_auth_path %>