code: public static function salt($name, $value) {
          // Require a valid salt
          if (!static::$salt) {
              $config = Mii::$app->config('cookie');
  
              if ($config AND isset($config['salt'])) {
                  static::$salt = $config['salt'];
              } else {
                  throw new InvalidArgumentException(
                      'A valid cookie salt is required. Please set Cookie::$salt before calling this method.' .
                      'For more information check the documentation'
                  );
              }
          }
  
          // Determine the user agent
          $agent = isset($_SERVER['HTTP_USER_AGENT']) ? strtolower($_SERVER['HTTP_USER_AGENT']) : 'unknown';
  
          return sha1($agent . $name . $value . static::$salt);
      }
docs: Generates a salt string for a cookie based on the name and value.
  
  $salt = Cookie::salt('theme', 'red');
  
  @param   string $name name of cookie
  @param   string $value value of cookie
  @return  string