This article, by settingAccess-Control-Allow-Originachieves cross-domain.

For example: the client's domain is client.example.com, while the requested domain is server.example.com.

If you access it directly using ajax, the following error will occur:

XMLHttpRequest cannot load http://server.example.com/server.php. No 'Access-Control-Allow-Origin' header is present on the requested resource.Origin 'http://client.example.com' is therefore not allowed access.

1. Allow a single domain to access

To allow a specific domain (http://client.example.com) cross-domain access, simply add the following code at the top of the http://server.example.com/server.php file:

header('Access-Control-Allow-Origin:http://client.example.com');

2. Allow multiple domains to access

To allow multiple domains (http://client1.example.com, http://client2.example.com, etc.) cross-domain access, simply add the following code at the top of the http://server.example.com/server.php file:

$origin = isset($_SERVER['HTTP_ORIGIN'])? $_SERVER['HTTP_ORIGIN'] : '';  
  
$allow_origin = array(  
    'http://client1.example.com',  
    'http://client2.example.com'  
);  
  
if(in_array($origin, $allow_origin)){  
    header('Access-Control-Allow-Origin:'.$origin);       
} 

3. Allow all domains to access

To allow all domains to access, simply add the following code at the top of the http://server.example.com/server.php file:

header('Access-Control-Allow-Origin:*');