rewrite ^/(.*)$ https://www.XXX.com/api/$1 permanent;

可以在api..com上配置反向代理指向 www..com/api/

server {
    ...
    server_name api.xxx.com;
    location / {
        proxy_pass www.xxx.com/api/;
    }
}

建议使用nginx代理，打开nginx.conf

增加一个新的server block

server {
    server_name api.xxx.com;
    location / {
        proxy_pass www.xxx.com/api/;
    }
}