set $root_domain "";

# Derive the apex domain from a www-prefixed primary server_name. This keeps the
# snippet simple, but it also means callers should not use it on multi-name
# server blocks whose first name is not the canonical www host.
if ($server_name ~* ^www\.(?<apex_domain>.+)$) {
	set $root_domain $apex_domain;
}

# Use 307 so POST and other non-GET methods keep their method during
# canonicalization instead of being rewritten to GET as with many 301/302 flows.
if ($host = $root_domain) {
	return 307 $scheme://$server_name$request_uri;
}