server {

    listen       80;

    server_name  www.your.com;

    root         /data/web/www.your.com;

    access_log   /var/log/nginx/www.your.com_access.log;

    error_log    /var/log/nginx/www.your.com_error.log;

    set $cors_origin "";

    if ( $http_origin ~ https?://.*\.(a|b)\.com ) {

        set $cors_origin $http_origin;

    }

    add_header Access-Control-Allow-Origin $cors_origin;

}

[root@HD1g-static-website /usr/local/nginx/conf/conf.d]# curl -I -H "Origin: https://test.a.com" https://www.your.com/a.jpg

HTTP/1.1 200 OK

Date: Sun, 05 May 2019 06:12:53 GMT

Content-Type: image/jpeg

Content-Length: 134100

Connection: keep-alive

Last-Modified: Tue, 05 Mar 2019 07:01:43 GMT

ETag: "5c7e1ed7-20bd4"

Expires: Tue, 04 Jun 2019 06:12:53 GMT

Cache-Control: max-age=2592000

Access-Control-Allow-Origin: https://test.a.com

Accept-Ranges: bytes

[root@HD1g-static-website /usr/local/nginx/conf/conf.d]# cat nginx_cors

if ($request_method = 'OPTIONS') {

    add_header 'Access-Control-Allow-Origin' '*';

    add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';

    #

    # Custom headers and headers various browsers *should* be OK with but aren't

    #

    add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';

    #

    # Tell client that this pre-flight info is valid for 20 days

    #

    add_header 'Access-Control-Max-Age' 1728000;

    add_header 'Content-Type' 'text/plain charset=UTF-8';

    add_header 'Content-Length' 0;

    return 204;

}

if ($request_method = 'POST') {

    add_header 'Access-Control-Allow-Origin' '*';

    add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';

    add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';

}

if ($request_method = 'GET') {

    add_header 'Access-Control-Allow-Origin' '*';

    add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';

    add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';

}