hmac nodejs esp8266

hmac.js

//https://github.com/rcarmo/azure-iot-esp-01-minimal-cpp/blob/master/iothub.cpp
//http://bitoftech.net/2014/12/15/secure-asp-net-web-api-using-api-key-authentication-hmac-authentication/

/*
var hmac = crypto.createHmac('sha256', secret_key);
hmac.update(request.body.message);
var signature = hmac.digest('hex'));
*/

var str        = payload_string;
var public_key = pk;
var secret_key = sk;

var hmac = crypto.createHmac('sha384', sk).update(str).digest('hex');

request.post({uri:..., json:{hmac:hmac, public_key:public_key, payload: str}, function(err, response, body){
   console.log(body);
});



exports.... = function(req, res)
{
   var hmac = req.body.hmac;
   var pk = req.body.public_key;
   var payload  = req.body.payload;


   // retrieve authorized user
   User.findOne({pk:pk},function(err, user){
      if(err || !user){
        return res.status(403).json({error:"Invalid user"});
      }
     else
     {

         // recompute hmac
         var compute_hmac= crypto.createHmac('sha384', user.sk).update(payload).digest('hex');

         // check hmac
         if(compute_hmac != hmac){
           return res.status(403).json({error:"Security check failed"});
         }
         else
         {
            // do stg
            return res.status(200).json({success:"ok"});
         }
      }
    });