Step 1
Download the cacert.pem file and place it into a some persistent folder.
Specify the filesystem location to the cacert.pem file in a PHP *.ini file with the curl.cainfo option:
curl.cainfo = "C:/server/pem/cacert.pem"
Source: http://stackoverflow.com/a/19149687
Step 2
Generate a self-signed certificate:
openssl genrsa -des3 -passout pass:x -out server.pass.key 2048
openssl rsa -passin pass:x -in server.pass.key -out server.key
rm server.pass.key
openssl req -new -key server.key -out server.csr
Leave the challenge password as empty.
openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt
Step 3
Add the contents of the generated server.crt file to the end of the cacert.pem file.
Source: http://serverfault.com/a/633647
Step 4
Restart PHP.