I use MAMP Pro for most of my PHP development and Chrome has annoyingly been blocking the self-signed SSL certificates MAMP generates, saying the certificate is not valid and "Your connection is not private": 

Thankfully, I found an easy solve to fix this. These steps assume you've created a host in MAMP. You'll need to go to the SSL tab of the host you are trying to fix and

Go back to Chrome, and reload the page and the certificate should work now: