Implementing facebook-OmniAuth using Rails

Create an application in Facebook to get the secret key. Next, you need to declare the provider in your (config/initializers/devise.rb) and require it:

require "omniauth-facebook"

config.omniauth :facebook, "APP_ID", "APP_SECRET"

make your model (e.g. app/models/user.rb) omniauthable:

devise :omniauthable

Now Devise will create the following url methods.

user_omniauth_authorize_path(provider)

user_omniauth_callback_path(provide)

Use the below line of code in your view file wherever you want to provide the Facebook link to authorize for the users:

<%= link_to "Sign in with Facebook", user_omniauth_authorize_path(:facebook) %>

When the user clicks on the above link, they will redirects to the Facebook login page, after entering their credentials it will again redirect the user back to our applications Callback method

When the user clicks on the above link, they will redirects to the Facebook login page, after entering their credentials it will again redirect the user back to our applications Callback method:

devise_for :users, :controllers => { :omniauth_callbacks => "users/omniauth_callbacks" }

Now we we are going to add a new controller file inside our Rails controller directory "app/controllers/users/omniauth_callbacks_controller.rb" and put the following line code in your omniauth_callbacks_controller.rb file.

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
  def facebook
    # You need to implement the method below in your model (e.g. app/models/user.rb)
    @user = User.find_for_facebook_oauth(request.env["omniauth.auth"], current_user) 
    if @user.persisted?
      sign_in_and_redirect @user, :event => :authentication #this will throw if @user is not activated
      set_flash_message(:notice, :success, :kind => "Facebook") if is_navigational_format?
    else
      session["devise.facebook_data"] = request.env["omniauth.auth"]
      redirect_to new_user_registration_url
    end
  end
end

Now we are going to implement the find_for_facebook_oauth method in our user model (e.g. app/models/user.rb) :

def self.find_for_facebook_oauth(auth, signed_in_resource=nil)
  user = User.where(:provider => auth.provider, :uid => auth.uid).first
  if user
    return user
  else
    registered_user = User.where(:email => auth.info.email).first
    if registered_user
      return registered_user
    else
      user = User.create(name:auth.extra.raw_info.name,
                                    provider:auth.provider,
                                    uid:auth.uid,
                                    email:auth.info.email,
                                    password:Devise.friendly_token[0,20]
                                  )
    end
  end
end