perl regex to extract "domain" and "extension" into variables from 'server_name' (no replies)

I want to extract just the "domain" and "extension" parts from an nginx
server_name for use as variables later in nginx conf.

For example,

server_name <some PERL regex ... ?<domain> ... ?<extension>
...>;
...
location = /test.html {
alias /local/path/to/$domain.$extension.html;
}

No matter what the server_name contains, from

mydomain.tld

to

https://www.mydomain.tld:80/something

and variations in between,the result should be

$domain = mydomain
$extension = tld

I found this post

"Perl Regex to get the root domain of a URL"
http://stackoverflow.com/questions/15627892/perl-regex-to-get-the-root-domain-of-a-url

that suggest this perl regex

^.*://(?:[wW]{3}\.)?([^:/]*).*$

works to extract & return "domain.tld" from any from of input URI.

What's the right form of that regex in nginx's server_name to populate
<domain> and <extension> variables for subsequent use?

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