code: @Nonnull
    public static ICommonsList <String> getAllClientCertIssuer ()
    {
      final ICommonsList <String> ret = new CommonsArrayList <> ();
  
      int nIndex = 1;
      while (true)
      {
        final String sValue = getConfigFile ().getAsString ("clientcert.issuer." + nIndex);
        if (StringHelper.hasNoText (sValue))
          break;
  
        // Present - try next
        ret.add (sValue);
        ++nIndex;
      }
      return ret;
    }
docs: Read value of <code>clientcert.issuer.X</code> values, where "X" is an
  ascending number starting from 1.
  
  @return The list of potential issuers of the expected client certificates.
  Never <code>null</code> but maybe empty.