unable to get local issuer certificate (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for https://oauth2.googleapis.com/token code example

Example: Fatal error: Uncaught GuzzleHttp\Exception\RequestException: cURL error 60: SSL certificate problem: unable to get local issuer certificate

1. Download the certificate bundle.

2. Put it somewhere. In my case, that was c:\wamp\ directory (if you are using 
	Wamp 64 bit then it's c:\wamp64\).

3. Enable mod_ssl in Apache and php_openssl.dll in php.ini (uncomment them by 
	removing ; at the beginning). But be careful, my problem was that I had two 
	php.ini files and I need to do this in both of them. One is the one you get 
	from your WAMP taskbar icon, and another one is, in my case, in 
	C:\wamp\bin\php\php5.5.12\

4. Add these lines to your cert in both php.ini files:
	curl.cainfo="C:/wamp/cacert.pem"	
    openssl.cafile="C:/wamp/cacert.pem"

5. Restart Wamp services.