Full Error
RequestException in CurlFactory.php line 187: cURL error 60: SSL certificate problem: unable to get local issuer certificate (see ht
This was stressfull to figure out but here is the exact answer for people using laravel and have this problem.
My exact application versions are...
Laravel: 5.4
Guzzlehttp: 6.2
Laravel Socialite: 3.0
Download a fresh copy of this curl certificate from this link: https://gist.github.com/VersatilityWerks/5719158/download
Save the file in this path starting from the base root of your laravel application vendor/guzzlehttp/guzzle/src/cacert.pem
next in that same directory open up RequestOptions.php and scroll down to the constant called CERT and change it to this const CERT = 'cacert.pem'; and this should fix it all.
EDIT
As people are pointing out you should never edit the vendor folder, this was just a quick fix for an application I was building in my spare time. It wasn't anything majorly important like an application for my company or anything, use this method at your own risk! Please check out the other answers if you need something more concrete.