It didn't used to support it not too long ago so I had to setup my server to explicitly not redirect to HTTPS for one particular location because people would need to install apt-transport-https for it.
EDIT: Over 12 years to be precise.
* added apt-transport-https method
Fri, 12 Jan 2007 20:48:07 +0100So in order to get the HTTPS transport, you needed to first download the required package over HTTP.