callback = function callback(error, result) {
      if (error) {
        response.json(401, error);
      } else if (result) {
        response.json(200, result);
      } else {
        response.json(400, {message: 'Given password does not match.'});
      }
    }
Main callback function which is called when all specified jobs are
processed or an error has occurred while processing.

@param   {null|Error}    error   Possible error
@param   {null|boolean}  result  If passport was valid or not