解决办法：

$opts = array(
    'http' => array(
        'method' => 'POST',
        'header' => 'content-type:application/json',
        'content' => file_get_contents($file)
    ),'ssl' => array(
        'verify_peer' => false,
        'verify_peer_name' => false,
        'allow_self_signed' => true
    )
);

$context = stream_context_create($opts);
$response_json = file_get_contents('https://opupload.com', false, $context);