Best method for constructing HTTPS urls and requiring HTTPS requests?

Some pages on my CI3 site (login, register, user cp, etc.) obviously need to be accessed via HTTPS. I did some searching and, if I'm not mistaken, a decision was made not to support https in base_url.

Can anyone tell me best practices for:
1) constructing site urls for links, form posting, redirects, etc. that require HTTPS
2) Configuring controllers and/or controller methods such that all requests must be via HTTPS?

Any help would be much appreciated.