🚨 2020 Update: I recommend using mkcert to generate local certificates. You can do everything below by just running the commands brew install mkcert and mkcert -install. Keep it simple!
This gives you that beautiful green lock in Chrome. I'm assuming you're putting your SSL documents in /etc/ssl, but you can put them anywhere and replace the references in the following commands. Tested successfully on Mac OS Sierra and High Sierra.
sudo nano /etc/ssl/localhost/localhost.conf