def create
      auth      = request.env["omniauth.auth"]
      user_auth = Authentication.find_by(provider: auth.provider,
                                         uid: auth.uid)

      return login(user_auth.person) if user_auth.present?

      add_authentication(auth) if signed_in?
      create_authentication(auth) unless signed_in?
    end
def create
      auth      = request.env["omniauth.auth"]
      user_auth = Authentication.find_by(provider: auth.provider,
                                         uid: auth.uid)

      return login(user_auth.person) if user_auth.present?

      add_authentication(auth) if signed_in?
      create_authentication(auth) unless signed_in?
    end
GET|POST /auth/facebook/callback