code: private static String getUniqueToken(String currentCapabilitiesHeader) {
          String token = "esigate";
  
          if (currentCapabilitiesHeader != null && currentCapabilitiesHeader.contains(token + "=\"")) {
              int id = 2;
              while (currentCapabilitiesHeader.contains(token + id + "=\"")) {
                  id++;
              }
              token = token + id;
          }
  
          return token;
      }
docs: Return a new token, unique for the current Surrogate-Capability header.
  <p>
  Uses "esigate" and appends a number if necessary.
  
  @param currentCapabilitiesHeader
  existing header which may contains tokens of other proxies (including other esigate instances).
  @return unique token