int pin_function(void *userdata, int attempt, const char *token_url,
                 const char *token_label, unsigned flags, char *pin, size_t pin_max)
{
  if (flags & GNUTLS_PIN_FINAL_TRY)
    printf("This is the final try before locking!\n");
  if (flags & GNUTLS_PIN_COUNT_LOW)
    printf("Only few tries left before locking!\n");
  if (flags & GNUTLS_PIN_WRONG)
    printf("Wrong PIN has been provided in the previous attempt\n");

  /* userdata is the second value passed to gnutls_pkcs11_set_pin_function()
   * in this example we passed the PIN as a null terminated value.
   */
  snprintf(pin, pin_max, "%s", (char*)userdata);
  return 0;
}