To determine the URL of a server, three components are needed:
the scheme (http? https?), the name and the port.
Generally, ports won't be the in URL, as they are the default
80 or 443 ports.
Advanced network configurations
Furthermore, in back-end/front-end topologies, To determine
if we're in HTTPS requires to examine several headers.
If there is now a standard, RFC 7239 section 4, a lot of load balancers,
caches or web servers use proprietary or former de facto headers.
Deprecation
The new Request::getServerURL method supersedes get_server_url
from Keruald/Xen sites like Azhàr or Zed.