SSL, Composer and PHP 5.6
A quick technical note: I ran into the same issue as Rob Allen did. Using his solution I came to understand the problem, but contrary to Rob, I was using an Ubuntu system in a Vagrant-box.
The solution is the same, the path is different. In your php.ini, you add/update the openssl.cafile parameter:
Don't forget to also restart Zend Server if you're going to use this through the webserver as well. Thanks Rob for your blogpost and Cees-Jan for finding the right path to this file.