Redirect www to not-www

[Paul]

Happy 2023 to all on this list.

Using nginx (1.18.0 on Ubuntu 20.04.5) as proxy to back-end, I have 
three sites (a|b|c.example.com) in a fast, reliable production 
environment. I have DNS records set up for www.a|b|c.example.com.  I 
have CertBot set up for only a|b|c.example.com.

To avoid "doubling" the number of sites-available and security scripts, 
and to avoid the unnecessary "www." I would like to add something like:

server {
   server_name www.a.example.com;
   return 301 $scheme://a.example.com$request_uri;
}

but I have tried this in several places, www.a.example.com works, but 
does not remove the www prefix, and fails any browser's security checks 
(nginx -t is "ok").

Where, in the following config, is the most elegant place to put such a 
"return" line?  Maybe I'm missing something fundamental?


server {
     listen 443 ssl;
                      [ ... # 4 lines managed by Certbot ... ]
     server_name a.example.com;    # Note: or b.example.com, or 
c.example.com
                      [ ... logging ... ]
     proxy_buffering off;
     if ($request_method !~ ^(GET|HEAD|POST)$) {
        return 444;
     }
     location / {
         proxy_pass http://192.168.x.y:port;
         proxy_set_header Host $host;
         proxy_http_version 1.1;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}
server {
     if ($host = a.example.com) {    # Note: or b.example.com, or 
c.example.com
         return 301 https://$host$request_uri;
     }
     listen 80;
     server_name a.example.com;      # Note: or b.example.com, or 
c.example.com
     rewrite     ^   https://$host$request_uri? permanent;
}

Many thanks -- Paul


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