SSL

If a website is unable to authenticate a valid peer certificate, download this file to the server:

https://curl.haxx.se/ca/cacert.pem

For more information about this file, see this page.

Then, you also need to setup the pem file in the PHP environment by placing this in the php.ini or .user.ini file:

openssl.cafile = "/full/path/to/file/cacert.pem"
curl.cainfo = "/full/path/to/file/cacert.pem"

Of course, make sure you replace /full/path/to/file/ with the path you downloaded the file above to.