Rails和Omniauth—应该从身份验证散列中保存多少数据?

I am currently using rails and the omniauth gem to integrate my application with facebook, twitter and linkedin. When I process an omniauth callback I simply save uid and provider from the authentication hash. Most tutorials online only save these fields as well but how would you be able to access the users details from facebook/twitter/linkedin later on? What other fields from the authentication hash should be saved other than uid/provider?I am currently using rails and the omniauth gem