So the requirement was such to allow to facebook login from the app , I chose omniauth facebook plugin for same .
Gems you need to define in your app are --
please notice the git links given beside the gems , believe me the default gems do not work for you . I had to google , regoogle try and find out stuff and finally !!! this is the correct combination of gems which you need for your tasks
Ok execute --
bundle install
And configure devise as provided in devise documentation
https://github.com/plataformatec/devise
Create omniauth.rb in configuration/initializers directory
place following code in the file
We will need to create one more model name Authentications to store authentication details of a user , in case he arrives from facebook
rails g model Authentications user_id:integer provider:string uid:string token:string
Maintain one to many relationship between authentications and user so here goes code accordingly
in authentications.rb
belongs_to user
in users.rb
has_many :authentications, :dependent => :delete_all
We need to add one callback controller function for omniauth to call . For the same purpose we will make one controller Authentications in our application
rails g controller Authentications
Create a method name "create" with in controller called while callback
I am maintaining a session variable over here to distinguish a fb session than a normal login session , you can follow some other approach of urs if you want
create apply_omniauth in user.rb
Configure route for Authentications Controller in routes.rb
match '/auth/facebook/callback' => 'authentications#create'
Finally place a link in your application.html.erb
<%= link_to "Sign in with Facebook", '/auth/facebook/'>
Alright so from here on you can successfully let people sign in with there fb accounts to your application
