code: function signIn (defOptions, credentials, callback) {
    var promise = normalizeRequestParameters(defaults, 'SignIn', credentials).then(function (credentials) {
  
      var options = {
        method : 'POST',
        uri : 'v1/SignIn',
        json : credentials
      };
      
      extend(true, options, defOptions);
      
      return options;
      
    }).then(request).nodeify(callback);
    
    return promise;
  }
docs: Sign in to Nfield API
  
  {@link https://api.nfieldmr.com/help/api/post-v1-signin}