Had the same error with PHP 7 on XAMPP and OSX.
The above mentioned answer in https://stackoverflow.com/ is good, but it did not completely solve the problem for me. I had to provide the complete certificate chain to make file_get_contents() work again. That's how I did it:
Get root / intermediate certificate
First of all I had to figure out what's the root and the intermediate certificate.
The most convenient way is maybe an online cert-tool like the ssl-shopper
There I found three certificates, one server-certificate and two chain-certificates (one is the root, the other one apparantly the intermediate).
All I need to do is just search the internet for both of them. In my case, this is the root:
thawte DV SSL SHA256 CA
And it leads to his url thawte.com. So I just put this cert into a textfile and did the same for the intermediate. Done.
Get the host certificate
Next thing I had to to is to download my server cert. On Linux or OS X it can be done with openssl:
openssl s_client -showcerts -connect whatsyoururl.de:443 </dev/null 2>/dev/null|openssl x509 -outform PEM > /tmp/whatsyoururl.de.cert
Now bring them all together
Now just merge all of them into one file. (Maybe it's good to just put them into one folder, I just merged them into one file). You can do it like this:
cat /tmp/thawteRoot.crt > /tmp/chain.crt
cat /tmp/thawteIntermediate.crt >> /tmp/chain.crt
cat /tmp/tmp/whatsyoururl.de.cert >> /tmp/chain.crt
tell PHP where to find the chain
There is this handy function openssl_get_cert_locations() that'll tell you, where PHP is looking for cert files. And there is this parameter, that will tell file_get_contents() where to look for cert files. Maybe both ways will work. I preferred the parameter way. (Compared to the solution mentioned above).
So this is now my PHP-Code
$arrContextOptions=array(
"ssl"=>array(
"cafile" => "/Applications/XAMPP/xamppfiles/share/openssl/certs/chain.pem",
"verify_peer"=> true,
"verify_peer_name"=> true,
),
);
$response = file_get_contents($myHttpsURL, 0, stream_context_create($arrContextOptions));
That's all. file_get_contents() is working again. Without CURL and hopefully without security flaws.