how to server over http and https with one installation

When you setup the SSL certificate for your domain on your web server, your WordPress site will immediately be accessible via http / https connections without any extra configuration.

Any configuration is required when you want your website or its backend (wp-admin / wp-login.php) to load ONLY via SSL (HTTPS).

But there’s at least one thing you should take care of:

  • Make sure your canonical URLs are either HTTP or HTTPS only (whichever you want to show up in search results). WordPress SEO by Yoast has an option to enforce this. Not sure, but WordPress HTTPS plugin may be of some help.