Given I have 2 subdomains configured in the DNS (so pinging both reply for both with the IP address of my server) and for those subdomains I have 2 different TLS certificates.

I have configured nginx this way:

```
# If we receive X-Forwarded-Proto, pass it through; otherwise, pass along the
# scheme used to connect to this server
map $http_x_forwarded_proto $proxy_x_forwarded_proto {
  default $http_x_forwarded_proto;
  ''      $scheme;
}

# If we receive Upgrade, set Connection to "upgrade"; otherwise, delete any
# Connection header that may have been passed to this server
map $http_upgrade $proxy_connection {
  default upgrade;
  ''      '';
}

gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript;

access_log /var/log/nginx.log;
error_log /var/log/nginx_errors.log;

# HTTP 1.1 support
proxy_http_version 1.1;
proxy_buffering off;
proxy_set_header Host $http_host;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $proxy_connection;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $proxy_x_forwarded_proto;

server {
  listen 80 default_server;
  server_name _; # This is just an invalid value which will never trigger on a real hostname.
  return 503;
  server_tokens off; # Hide the nginx version
}

upstream sub1.domain.tld {
  server 172.17.0.27:5000;
}

server {
  server_name sub1.domain.tld;
  server_tokens off; # Hide the nginx version

  listen 443 ssl;
  ssl_certificate /etc/nginx/ssl/sub1.domain.tld.crt;
  ssl_certificate_key /etc/nginx/ssl/sub1.domain.tld.key;

  location / {
    auth_basic "Restricted";
    auth_basic_user_file /etc/nginx/htpasswd/sub1.htpasswd;
    proxy_pass http://sub1.domain.tld;
  }
}

```

At this point, if I go to `https://sub1.domain.tld` all is working fine.
Now if I try to access `https://sub2.domain.tld` which is not yet configured and so should not reply it accept the connection and show me an issue with the certificate as it doesn't match the server name, so it seems that with this configuration, Nginx send the certificate for all request to the 443 port.

How should I change my configuration so that accessing `https://sub2.domain.tld` fail (with a 503 error for example) until I configure it by adding a new `server` instruction ?