code: public BackchannelAuthenticationResponse callBackchannelAuthentication(
              MultivaluedMap<String, String> parameters, String clientId, String clientSecret,
              String clientCertificate, String[] clientCertificatePath)
      {
          String params = URLCoder.formUrlEncode(parameters);
  
          return callBackchannelAuthentication(params, clientId, clientSecret, clientCertificate, clientCertificatePath);
      }
docs: Call Authlete's {@code /api/backchannel/authentication} API.