I found a bunch of different instructions, but these are the instructions that actually worked for me (regular Mac running Apache server) to get https working (self-signed certificate, so you will get the certificate warning from your web browser):

Step 1

Self-signed SSL Certificate on Mac Yosemite

Step 2

Enable HTTPS in Apache on Mac Yosemite

Step 3

Step 2 gave me an error (AH00526: Syntax error on line 73 of /private/etc/apache2/extra/httpd-ssl.conf:
SSLSessionCache: ‘shmcb’ session cache not supported (known names: ). Maybe you need to load the appropriate socache module (mod_socache_shmcb?).), so I edited the /private/etc/apache2/httpd-conf and followed these instructions.