MAGETWO-61531: Paypal SSL Curl communication error, TLS 1.2 required for https://*.paypal.com

- adding configurable curl minimum tls 1.2 version

lib/internal/Magento/Framework/HTTP/Client/Curl.php

@@ -9,14 +9,17 @@ namespace Magento\Framework\HTTP\Client;
  * Class to work with HTTP protocol using curl library
  *
  * @author      Magento Core Team <core@magentocommerce.com>
+ * @SuppressWarnings(PHPMD.ExcessiveClassComplexity)
  */
 class Curl implements \Magento\Framework\HTTP\ClientInterface
 {
+    const SSL_VERSION = 6;
+
     /**
      * Max supported protocol by curl CURL_SSLVERSION_TLSv1_2
      * @var int
      */
-    private static $sslVersion = 6;
+    private $sslVersion;
 
     /**
      * Hostname
@@ -86,7 +89,7 @@ class Curl implements \Magento\Framework\HTTP\ClientInterface
 
     /**
      * Curl
-     * @var object
+     * @var resource
      */
     protected $_ch;
 
@@ -117,10 +120,11 @@ class Curl implements \Magento\Framework\HTTP\ClientInterface
     }
 
     /**
-     * Constructor
+     * @param int|null $sslVersion
      */
-    public function __construct()
+    public function __construct($sslVersion = null)
     {
+        $this->sslVersion = $sslVersion;
     }
 
     /**
@@ -377,10 +381,9 @@ class Curl implements \Magento\Framework\HTTP\ClientInterface
             $this->curlOption(CURLOPT_PORT, $this->_port);
         }
 
-        //$this->curlOption(CURLOPT_HEADER, 1);
         $this->curlOption(CURLOPT_RETURNTRANSFER, 1);
         $this->curlOption(CURLOPT_HEADERFUNCTION, [$this, 'parseHeaders']);
-        $this->curlOption(CURLOPT_SSLVERSION, self::$sslVersion);
+        $this->setSSLVersion($this->sslVersion);
 
         if (count($this->_curlUserOptions)) {
             foreach ($this->_curlUserOptions as $k => $v) {
@@ -415,6 +418,7 @@ class Curl implements \Magento\Framework\HTTP\ClientInterface
      * @param resource $ch curl handle, not needed
      * @param string $data
      * @return int
+     * @throws \Exception
      * @SuppressWarnings(PHPMD.UnusedFormalParameter)
      */
     protected function parseHeaders($ch, $data)
@@ -422,11 +426,10 @@ class Curl implements \Magento\Framework\HTTP\ClientInterface
         if ($this->_headerCount == 0) {
             $line = explode(" ", trim($data), 3);
             if (count($line) != 3) {
-                return $this->doError("Invalid response line returned from server: " . $data);
+                $this->doError("Invalid response line returned from server: " . $data);
             }
             $this->_responseStatus = intval($line[1]);
         } else {
-            //var_dump($data);
             $name = $value = '';
             $out = explode(": ", trim($data), 2);
             if (count($out) == 2) {
@@ -493,4 +496,19 @@ class Curl implements \Magento\Framework\HTTP\ClientInterface
     {
         $this->_curlUserOptions[$name] = $value;
     }
+
+    /**
+     * Set ssl version to specified version or default
+     *
+     * @param int $sslVersion
+     * @return void
+     */
+    private function setSSLVersion($sslVersion)
+    {
+        if ($sslVersion) {
+            $this->sslVersion = $sslVersion;
+        } else {
+            $this->sslVersion = self::SSL_VERSION;
+        }
+    }
 }