code: private String formatPolicy() {
          final StringBuilder sb = new StringBuilder();
          sb.append("pin-sha256").append("=\"").append(primaryHash).append("\"; ");
          sb.append("pin-sha256").append("=\"").append(backupHash).append("\"; ");
          sb.append("max-age").append("=").append(maxAge);
  
          if (includeSubdomains) {
              sb.append("; ").append("includeSubDomains");
          }
  
          if (reportUri != null) {
              sb.append("; ").append("report-uri").append("=\"").append(reportUri).append("\"");
          }
          return sb.toString();
      }
docs: Formats the HPKP policy header.
  @return a properly formatted HPKP header