Rob Allen has a quick tip posted today about SSL certificate verification in PHP 5.6 and things that need to be updated thanks to recent improvements in PHP's SSL handling.
I recently updated my local OS X Zend Server installation to PHP 5.6 and when I ran composer self-update, I got this error message: "The "https://getcomposer.org/version" file could not be downloaded: SSL operation failed" [...] Googling around, I finally worked out that there have been various SSL improvements in PHP 5.6 and that the problem was that it couldn't find any OpenSSL certificates on my system. This isn't a total surprise as OS X has been moving away from using OpenSSL internally in favour of its own libraries.
To resolve the issue he found where PHP was looking for certificates (using openssl_get_cert_locations) and how a quick "brew install" of the needed OpenSSL handling resolved the issue. Then, in the php.ini file a quick update to the "openssl.cafile" path points it to the right certificate.