add DEBUG switch and fix win build error

core/src/CurlHttpClient.cc

@@ -15,6 +15,7 @@
  */
 
 #include "CurlHttpClient.h"
+#include "Utils.h"
 #include <cassert>
 #include <sstream>
 #include <string>
@@ -124,6 +125,10 @@ CurlHttpClient::makeRequest(const HttpRequest &request) {
   curl_easy_setopt(curlHandle_, CURLOPT_WRITEFUNCTION, recvBody);
   setCUrlProxy(curlHandle_, proxy());
 
+  if (GetEnv("DEBUG") == "sdk") {
+    curl_easy_setopt(curlHandle_, CURLOPT_VERBOSE, 1L);
+  }
+
   CURLcode res = curl_easy_perform(curlHandle_);
   switch (res) {
   case CURLE_OK: {