当浏览器发起ajax请求到其他域名时,会出现跨域的问题,在nginx上的解决方案是配置Access-Control-Allow-Origin来解决,此参数只允许配置单个域名或者*，当我们需要允许多个域名跨域访问时却不好配置,可以用map来实现

map $http_origin $corsHost {
    default 0;
    "~http://www.123admin.com" http://www.123admin.com;
    "~http://m.123admin.com" http://m.123admin.com;
    "~http://wap.123admin.com" http://wap.123admin.com;
}
server
{
    listen 80;
    server_name search.123admin.com;
    root /nginx;
    location /
    {
        add_header Access-Control-Allow-Origin $corsHost;
    }
}