Adding Facebook Login to a Rails application

rails_app_facebook_login_guide.md

Configuring a Rails app to use facebook sign in###

First of all: Im folliwing this tutorial from Rails Casts to do the implementation of facebook:

Creating the application: rails new facebook_oauth
Moving to the directory: cd facebook_oauth
Add the omniauth gem to your Gemfile: gem ‘omniauth’
In your terminal, run bundle

Create the file config/initializers/omniauth.rb and add:

Rails.application.config.middleware.use OmniAuth::Builder do  
    provider :facebook, 'CONSUMER_KEY', 'CONSUMER_SECRET'  
end

Substitute the key and secret for the secret and key of your registered application. You’ll need to hide this in the future.

Starting the server rails s gives the following error: warning: already initialized constant APP_PATH
I commented the line where the gem “spring” is. Looks like this gem is causing the problem. Run bundle in terminal. Now I get another error:

`Could not find matching strategy for :facebook. You may 	need to install an additional gem (such as omniauth-		facebook)`

Addind gem omniauth-facebook to Gemfile. Running bundle in terminal. Running rails s on the terminal is now working.

Run in your console rails g controller StaticPages index. Modify your config/routes file and change the root: root 'static_page#index'

Add to application.html.erb

<%= link_to “Sign in with facebook”, “/auth/facebook” %>

You also need a route for the callback from facebook. Modify you config/routes in order to create a route:

match 'auth/facebook/callback' => 'sessions#create', via: 'get'

You need to create a sessions controller: rails g controller sessions create Also you need to create a models for the users: rails g model user provider:string uid:string name:string
(The privider and uid fields seems to be mandatory but the name is optinal and we added here to have some extra info about the user).
After that we need to migrate the database: rake db:migrate
Inside the sessions_controller.rb you need to add to you create method:

def create
  auth = request.env["omniauth.auth"]
  user = User.find_by_provider_and_uid(auth['provider'], auth['uid']) || User.create_with_omniauth(auth)
end

In this code, auth is the data about the user that we get from facebook. You can take a look at it by writing raise request.env["omniauth.auth"].to_yaml in the same method in the controller.

We are trying to find a user by two parameters: provider and uid. If we can not find it, we'll create it using the method create_with_omniauth that we'll define in the User.rb model class.

In models/user.rb:

def self.create_with_omniauth(auth)
  create! do |user|
    user.provider = auth["provider"]
    user.uid = auth["uid"]
    user.name = auth["info"]["name"]
  end
end

(Careful with syntax errors...)

Add these couple of lines to the sessions#create method:

session[:user_id] = user.id
redirect_to root_url, notice: "Signed in"

In your application_controller.rb:

helper_method :current_user

  private

  def current_user
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end

In your application.html.erb:

<% if current_user %>
  Welcome, <%= current_user.name%>
  <%= link_to "Sign out", signout_path %
<% else %>
  <%= link_to "Sign in with facebook", "/auth/facebook" %>
<% end %>

In your config/routes.rb:

 match '/signout' => 'sessions#destroy', via: :get, as: :signout

Finally in the sessions_controller;

def destroy
  session[:user_id] = nil
  redirect_to root_url, notice: "Signed out"
end