referralsaasquatch node.js integration

referralsaasquatch_node.js

    // this relies or lodash or underscore
    // based on algorithm here http://docs.referralsaasquatch.com/squatchjs/signed-requests
    var params = req.body;

    // delete any null keys http://stackoverflow.com/questions/14058193/remove-empty-properties-falsy-values-from-object-with-underscore-js
    var clean_params = _.pick(params, _.identity);

    // sort keys and join to add to string
    var params_to_sign_string = '' ;

    _.forEach(_.keys(clean_params).sort(), function(key_name){
      params_to_sign_string += params[key_name];
    });

    // sign stackoverflow.com/questions/20004530/node-js-hmac-sha256-base64-of-string
    var hash = crypto.createHmac('SHA256', config.referralsaasquatch.api_key).update(params_to_sign_string).digest('base64'); 

    var response = {
      checksum: hash
    };