Install and use

1. Install the facebooker2 plugin and make Rails use it

Information on this installation here: https://github.com/mmangino/facebooker2

2. Install the Authlogic Facebook Connect plugin

$ script/plugin install git://github.com/studybyte/authlogic_facebook_connect.git

3. Make some changes to your database

class AddFacebookConnectFieldsToUser < ActiveRecord::Migration
  def self.up
    add_column :users, :facebook_session_key, :string
    add_column :users, :facebook_uid, :integer
  end

  def self.down
    remove_column :users, :facebook_uid
    remove_column :users, :facebook_session_key
  end
end

4. Make your layout look something like this

Add the <%= fb_connect_async_js %> tag to your application template

5. Add the Facebook Connect button to your login form

<%= authlogic_facebook_login_button %>
Options:
  :controller => The controller of you user session
  Any of the options for the fb login button here: http://developers.facebook.com/docs/reference/plugins/login

Notes

If you want to save some user data when connecting to facebook you can use the before_connect hook in your user model.

def before_connect(facebook_session)
  self.first_name = facebook_session.first_name
  self.last_name = facebook_session.last_name
  self.email = facebook_session.email
  self.username = "#{facebook_session.first_name}.#{facebook_session.last_name}"
  self.password = Digest::SHA1.hexdigest("--#{Time.now.to_s}--#{self.username}--")[0,6]
  self.password_confirmation = self.password
  self.active = true
end

For more information about what you can get form the facebook_session checkout the Facebooker gem rdoc.

Authenticating existing users

If you would like to have existing users of you application to connect to their facebook accounts do the following:

Be sure in your users session controller you don't have the `create` action in the require_no_login before_filter. Then make you create action look something like this:

def create
  if current_user
    if current_user_session.associatable_with_facebook_connect?
      if current_user_session.associate_with_facebook_connect
        flash[:notice] = "Your account is now associated with your facebook account"
        redirect_to root_url
      end
    else
      flash[:notice] = "Your facebook account is already connected"
      redirect_to profile_url
    end
  else
    @user_session = UserSession.new(params[:profile_session])
    if @user_session.save
      flash[:notice] = "Login successful!"
      redirect_to root_url
    else
      if @user_session.errors.on(:facebook)
        flash[:notice] = "An account already exists with this email, please login to connect it with your Facebook account."
        redirect_to login_path
      else
        flash[:notice] = "Could not login."
        render :action => :new
      end
    end
  end
end

This will make the user login to their account first before connecting with their facebook, if a user with the same email already exists. When clicking the Facebook connect button while logged in it will connect their accounts and from then on they will be able to login with facebook.