Create example of requesting security pin when ble connecting

Created topic: https://forum.arduino.cc/t/arduinoble-clarification-and-examples-about-ble-security/1093188 But no response for this moment. Currently I'm stuck with this issue. I've spend couple days on analyzing ArduinoBLE and can't create solution for requesting pin when ble connecting. Lets create example for future developers. It additionally unblock me to finish work at open source BLE firmware uploads library. For NimBLE-Arduino library I'm using:

BLEDevice::setSecurityPasskey(123456);
BLEDevice::setSecurityAuth(true, true, true); // bonding, mitm, sc 
BLEDevice::setSecurityIOCap(BLE_HS_IO_DISPLAY_ONLY);

And start security on connected callback:

void ArduinoBleOTAClass::onConnect(BLEServer* pServer, ble_gap_conn_desc* desc)
{
  BLEDevice::startSecurity(desc->conn_handle);
}

Initially at ArduinoBLE, as I see, to achieve BLE_HS_IO_DISPLAY_ONLY we shoud BLE.setDisplayCode() and not BLE.setBinaryConfirmPairing(). How to start security when ble connecting?

arduino-libraries / ArduinoBLE

Create example of requesting security pin when ble connecting #289