Acquia Dev Desktop, PHP 5.6 and SSL certificate issue on local MacOSX
After looking around I found kenorb's reply on a similar issue:
https://drupal.stackexchange.com/a/149456/62500

and after poking around the DevDesktop installed files on my Mac I managed to solve it.

The problem is the certificate file does not exist at the default location. 

print_r(openssl_get_cert_locations());


Returns

Array ( 
    [default_cert_file] =&gt; /Users/acquia/csbworkdir/dmitrybezer/libopenssl/install/ssl/cert.pem 
    [default_cert_file_env] =&gt; SSL_CERT_FILE 
    [default_cert_dir] =&gt; /Users/acquia/csbworkdir/dmitrybezer/libopenssl/install/ssl/certs 
    [default_cert_dir_env] =&gt; SSL_CERT_DIR 
    [default_private_dir] =&gt; /Users/acquia/csbworkdir/dmitrybezer/libopenssl/install/ssl/private 
    [default_default_cert_area] =&gt; /Users/acquia/csbworkdir/dmitrybezer/libopenssl/install/ssl 
    [ini_cafile] =&gt; [ini_capath] =&gt; ) 


So it is looking for cert.pem in the non existent directory "/Users/acquia/csbworkdir/dmitrybezer/libopenssl/install/ssl/"

To solve this, edit /Applications/[Dev desktop folder]/php5_6/bin/php.ini

and add these lines:

[openssl]
openssl.cafile="/Applications/[Dev desktop folder]/common/cert/cacert.pem"
openssl.capath="/Applications/[Dev desktop folder]/common/cert/"


where is [Dev desktop folder] is the name of your Dev Desktop folder.