limit_req_zone based on subdomain key

[grayaii]

We want to rate limit based on subdomain.
Is this possible? If so, how do you it?

Basically, what goes here?

limit_req_zone $XXXXXXX zone=mylimit:10m rate=10r/s;
 
server {
    location /login/ {
        limit_req zone=mylimit;
        
        proxy_pass http://my_upstream;
    }
}

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,285355,285355#msg-285355