def login(user, &block)
      authenticate_session.login user, &block

      if logged_in? && Authenticate.configuration.rotate_csrf_on_sign_in?
        session.delete(:_csrf_token)
        form_authenticity_token
      end
    end
def login(user, &block)
      authenticate_session.login user, &block

      if logged_in? && Authenticate.configuration.rotate_csrf_on_sign_in?
        session.delete(:_csrf_token)
        form_authenticity_token
      end
    end
Complete the user's sign in process: after calling authenticate, or after user creates account.
 Runs all valid callbacks and sends the user a session token.