code: function(cb) {
          var at = this.brain.get(this.TOKEN_KEY),
              rt = this.brain.get(this.REFRESH_KEY);
  
          if (at == null || rt == null) {
  
              cb({
                  err: null,
                  msg: 'Error: No tokens found. Please authorize this app and store a refresh token'
              });
              return;
          }
  
          var expirTime = this.brain.get(this.EXPIRY_KEY),
              curTime = (new Date()) / 1;
  
          var self = this;
          if (expirTime < curTime) {
              this.oauthClient.refreshAccessToken(function(err, token) {
                  if (err != null) {
                      cb({
                          err: err,
                          msg: 'Google Authentication Error: error refreshing token'
                      }, null);
                      return;
                  }
  
                  self.storeToken(token);
                  cb(null, {
                      resp: token,
                      msg: 'Token refreshed'
                  });
              });
          } else {
              cb(null);
          }
      }
docs: Checks the current expire time and determines if the token is valid.
  Refreshes the token if it is not valid.
  
  @param  cb  the callback function (err, resp), use this to make api calls