跨域资源共享（CORS）-浏览器同源政策

1. http://www.ruanyifeng.com/blog/2016/04/same-origin-policy.html
2. http://www.ruanyifeng.com/blog/2016/04/cors.html
   
3. https://developer.mozilla.org/en-US/docs/Web/HTTP/Server-Side_Access_Control
   
4.