RailsでFacebookログイン
1.OmniAuthをインストール
gem 'omniauth'
2.Facebook Developer登録
https://developers.facebook.com/apps
⇒新しいアプリを作成
⇒URLはHerokuなどで生成
https://www.heroku.com/
3.FacebookAPIキー設定
/config/initializers/omniauth.rb
Rails.application.config.middleware.use OmniAuth::Builder do provider :twitter,"Consumer key","Consumer secret" provider :facebook,"App ID","App Secret" end