How can I set the Access-Control-Allow-Origin header?

Question

I know this is a really simple question, but after searching a lot I can't find how to set headers.

Here's what I want to do:

Whenever the user goes to https://www.google.com/ , then an extension should log that into a logfile. I currently am developing the extension on my own device, and using http://localhost/log.php to get POST requests and log information to files based on the information POSTed. My manifest is working and I have tested it. Below is my track.js :

function log(info){
    var xhttp=new XMLHttpRequest();
    xhttp.onreadystatechange=function(){
        if(this.readyState===4&&this.status===200){
            console.log(this.responseText);
        }
    }
    xhttp.open("POST","http://localhost/log.php",true);

    // xhttp.setRequestHeader("Access-Control-Allow-Origin","*");
    // above: my first attempt to set a header (did not work)

    xhttp.send("log_info="+info);
}
if(location.href==="https://www.google.com/")log("We're at google.com!");

This is my log.php :

<?php
header("Access-Control-Allow-Origin: *");
if(isset($_POST["log_item"]))
    file_put_contents("log.txt", $_POST["log_item"]."\n",FILE_APPEND);

And log.txt is an empty file. I know CORS is the problem because when I open the console on https://www.google.com/ , I see this:

Access to XMLHttpRequest at 'http://localhost/log.php' from origin 'https://www.google.com' has been blocked by CORS policy: Request header field access-control-allow-origin is not allowed by Access-Control-Allow-Headers in preflight response.

POST http://localhost/log.php net::ERR_FAILED

This seems really simple to me but I can't find how to set headers. Thanks for any help.

Answer 1

You should add "Access-Control-Allow-Origin: *" on your webserver configuration (Nginx or Apache or...) that you are currently using on your localhost.

You can not bypass CORS from your code or your request at all.

For nginx (/etc/nginx/nginx.conf):

https://enable-cors.org/server_nginx.html

Apache:

https://enable-cors.org/server_apache.html