json - Vue Axios CORS policy: No 'Access-Control-Allow-Origin'

Question

I build an app use vue and codeigniter, but I have a problem when I try to get api, I got this error on console

Access to XMLHttpRequest at 'http://localhost:8888/project/login' 
from origin 'http://localhost:8080' has been blocked by CORS policy: 
Request header field access-control-allow-origin is not allowed 
by Access-Control-Allow-Headers in preflight response.

I have been try like this on front-end (main.js)

axios.defaults.headers.common['Content-Type'] = 'application/x-www-form-urlencoded'
axios.defaults.headers.common['Access-Control-Allow-Origin'] = '*';

and this on backend (controller)

header('Access-Control-Allow-Origin: *');
header("Access-Control-Allow-Methods: GET, POST, OPTIONS, PUT, DELETE");

and vue login method

this.axios.post('http://localhost:8888/project/login', this.data, {
   headers: {
          "Access-Control-Allow-Origin": "*",
          "Access-Control-Allow-Methods": "GET, POST, PATCH, PUT, DELETE, OPTIONS",
          "Access-Control-Allow-Headers": "Origin, Content-Type, X-Auth-Token"
        }
      }).then(res => {
        console.log(res);
      }).catch(err => {
        console.log(err.response);
      });

I've searched and tried in stackoverflow but does not work, how I can solve it? thank you so much for your help

Answer 1

CORS is the server telling the client what kind of HTTP requests the client is allowed to make. Anytime you see a Access-Control-Allow-* header, those should be sent by the server, NOT the client. The server is "allowing" the client to send certain headers. It doesn't make sense for the client to give itself permission. So remove these headers from your frontend code.

axios.defaults.headers.common['Access-Control-Allow-Origin'] = '*';

this.axios.post('http://localhost:8888/project/login', this.data, {
   headers: {
          // remove headers
        }
      }).then(res => {
        console.log(res);
      }).catch(err => {
        console.log(err.response);
      });

For example, imagine your backend set this cors header.

header("Access-Control-Allow-Methods: GET");

That means a client from a different origin is only allowed to send GET requests, so axios.get would work, axios.post would fail, axios.delete would fail, etc.