Adds OmniAuth support to your model.
Oauthable adds the following options to devise_for:
* +omniauth_providers+: Which providers are avaialble to this model. It expects an array: devise_for :database_authenticatable, :omniauthable, :omniauth_providers => [:twitter]
# File lib/devise/models/omniauthable.rb, line 18 def self.required_fields(klass) [] end