用ajax POST设计

Question

I can't access current_user in my api controller when sending a POST request. It says it is null.

class ApiController < ApplicationController
    before_action :set_default_format
    skip_before_action :verify_authenticity_token

    private
        def set_default_format
            request.format = :json
        end
end

class Api::V1::PhotosController < ApiController
...
end

What am I doing wrong? I read a couple of posts on SO and the solutions do not work.