code: function (req, res, next) {
      var userId = req[this.paramName]._id;
      var oldPass = String(req.body.oldPassword);
      var newPass = String(req.body.newPassword);
  
      this.model.findOne({'_id': userId}, function (err, user) {
        if (user.authenticate(oldPass)) {
          user.password = newPass;
  
          user.save(function (err) {
            if (err) {
              return res.handleError(err);
            }
            return res.noContent();
          });
        } else {
          res.forbidden();
        }
      });
    }
docs: Change the password of a user in the DB. The 'oldPassword' and 'newPassword' property of the
  request body are used.
  @param {IncomingMessage} req - The request message object containing the 'oldPassword' and 'newPassword' property
  @param {ServerResponse} res - The outgoing response object
  @param {function} next - The next handler function
  @returns {ServerResponse} The response status OK or FORBIDDEN if an error occurs