curl postfields to request body are not passing thru

The lib_curl_http.h file in the include dir needs an extra setting to allow POSTFields to be passed to the body of the request.
SPN token only works if we post the client_credential params to the body of the message not as params.
In http://github.com/azure/azure-storage-fuse We added this line to get the above working.
check_code(curl_easy_setopt(m_curl, CURLOPT_POSTFIELDS, nullptr)); // CURL won't actually read data on POSTs unless this is explicitly set.

See our working method below.

void set_input_stream(storage_istream s) override {
m_input_stream = s;
check_code(curl_easy_setopt(m_curl, CURLOPT_READFUNCTION, read));
check_code(curl_easy_setopt(m_curl, CURLOPT_READDATA, this));
check_code(curl_easy_setopt(m_curl, CURLOPT_POSTFIELDS, nullptr)); // CURL won't actually read data on POSTs unless this is explicitly set.
}