Setup for Devise + Omniauth (mongoid and facebook-only)

01. Gemfile

#add this to your gemfile
gem 'mongoid'
gem 'devise'
gem "omniauth-facebook"

02. Install devise, generate user and authorization models

rails g devise:install
#after installing devise look at the configs it needs (will be shown in the console output)

rails g devise user

rails g model authorization provider:string uid:string user_id:integer token:string secret:string name:string link:string

authorization.rb

# app/models/authorization.rb

class Authorization
  include Mongoid::Document
	field :provider, type: String
	field :uid, type: String
	field :user_id, type: Integer
	field :token, type: String
	field :secret, type: String
	field :name, type: String
	field :link, type: String

        #simply add this, the above code will be generated for you XD
	belongs_to :user
end

devise.rb

# app/config/initializers/devise.rb

Devise.setup do |config|
...
  config.omniauth :facebook, "KEY", "SECRET"
...
end

omniauth_callbacks_controller.rb

class OmniauthCallbacksController < Devise::OmniauthCallbacksController
  def facebook
    oauthorize "Facebook"
  end

private
  def oauthorize(kind)
    @user = find_for_ouath(kind, env["omniauth.auth"], current_user)
    if @user
      flash[:notice] = I18n.t "devise.omniauth_callbacks.success", :kind => kind
      session["devise.#{kind.downcase}_data"] = env["omniauth.auth"]
      sign_in_and_redirect @user, :event => :authentication
    end
  end
  def find_for_ouath(provider, access_token, resource=nil)
    user, email, name, uid, auth_attr = nil, nil, nil, {}
    case provider
    when "Facebook"
      uid = access_token['uid']
      email = access_token['info']['email']
      auth_attr = { :uid => uid, :token => access_token['credentials']['token'], :secret => nil, :name => access_token['info']['name'], :link => access_token['info']['link'] }
    else
      raise 'Provider #{provider} not handled'
    end

    if resource.nil?
      if email
        user = find_for_oauth_by_email(email, resource)
      else
        raise "Email not provided"
      end
    else
      user = resource
    end

    auth = user.authorizations.select{|a| a.provider == provider}
    if auth.nil? or auth.blank?
      auth = user.authorizations.build(:provider => provider)
      user.authorizations << auth
      user.save
    end
    auth.update_attributes auth_attr

    return user
  end
  def find_for_oauth_by_email(email, resource=nil)
    if user = User.find_by(email: email)
      user
    else
      user = User.new(:email => email, :password => Devise.friendly_token[0,20])
      user.password_confirmation = user.password
      user.save!
    end
    return user
  end
end

routes.rb

devise_for :users, :path => "accounts", :controllers => { :omniauth_callbacks => "omniauth_callbacks"}

user.rb

class User
  include Mongoid::Document
  devise :database_authenticatable,
         :trackable, :validatable, :omniauthable

  ## Database authenticatable
  field :name,              :type => String, :default => ""
  field :email,              :type => String, :default => ""
  field :encrypted_password, :type => String, :default => ""

  validates_presence_of :email
  validates_presence_of :encrypted_password

  ## Trackable
  field :sign_in_count,      :type => Integer, :default => 0
  field :current_sign_in_at, :type => Time
  field :last_sign_in_at,    :type => Time
  field :current_sign_in_ip, :type => String
  field :last_sign_in_ip,    :type => String

  has_many :authorizations, :dependent => :destroy
end