code: public function salt(string $name, string $value): string {
          // Require a valid salt
          if (!$this->cookie_salt) {
              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 . $this->cookie_salt);
      }
docs: Generates a salt string for a cookie based on the name and value.
  
  @param   string $name name of cookie
  @param   string $value value of cookie
  @return  string