code: private String formatHeader() {
          final StringBuilder sb = new StringBuilder();
          getStringFromValue(sb, "default-src", defaultSrc);
          getStringFromValue(sb, "script-src", scriptSrc);
          getStringFromValue(sb, "style-src", styleSrc);
          getStringFromValue(sb, "img-src", imgSrc);
          getStringFromValue(sb, "connect-src", connectSrc);
          getStringFromValue(sb, "font-src", fontSrc);
          getStringFromValue(sb, "object-src", objectSrc);
          getStringFromValue(sb, "media-src", mediaSrc);
          getStringFromValue(sb, "frame-src", frameSrc);
          getStringFromValue(sb, "sandbox", sandbox);
          getStringFromValue(sb, "report-uri", reportUri);
          getStringFromValue(sb, "child-src", childSrc);
          getStringFromValue(sb, "form-action", formAction);
          getStringFromValue(sb, "frame-ancestors", frameAncestors);
          getStringFromValue(sb, "plugin-types", pluginTypes);
          return sb.toString().replaceAll("(\\[|\\])", "").trim();
      }
docs: Formats a CSP header
  @return a String representation of CSP header