Google authentication with 'signet' ruby gem

We will implement google authentication with 'signet' gem. It is official ruby gem of google. It support  OAuth 1.0 / OAuth 2.0 implementation.

So, in Gemfile.

  gem 'signet'

run bundle.

Now, we have to create a google application on google developer console. This will provide us app_id, client_id and client_secret.

After that we will initialize the client of google auth for particular user.

In User.rb

  def initialize_google_client
    client = Signet::OAuth2::Client.new(
        :authorization_uri => 'https://accounts.google.com/o/oauth2/auth',
        :token_credential_uri =>  'https://www.googleapis.com/oauth2/v3/token',
        :client_id => 'Your client Id is here',
        :client_secret => 'Your client secret is here',
        :scope => 'email profile',
        :redirect_uri => 'redirect url same as you have put in your google     application'
    )
  end

In above initializer you can add scope as per your requirement.

Now, we will create routes for authentication path and callback redirect path.

In routes.rb

  get '/google_auth'=> 'some_controller#google_auth', as: 'google_authentication'
  get 'google_callback' => 'some_controller#google_callback'

Now, in controller -

  def google_auth
    client = current_user.initialize_google_client
    redirect_to(client.authorization_uri)
  end

  def google_callback
    client = current_user.initialize_google_client
    client.code = request['code']
    token = client.fetch_access_token!
  end

Above method provide you, access_token, refresh_token and id_token for particular user.