The purpose of the functions in NimBLEServerCallbacks.

[goddade]

What is the purpose of the security callback functions in the NimBLE_Server example? NimBLE_Secure_Server does not have callback functions.

    /********************* Security handled here *********************/
    uint32_t onPassKeyDisplay() override {
        Serial.printf("Server Passkey Display\n");
        /**
         * This should return a random 6 digit number for security
         *  or make your own static passkey as done here.
         */
        return 123456;
    }

    void onConfirmPassKey(NimBLEConnInfo& connInfo, uint32_t pass_key) override {
        Serial.printf("The passkey YES/NO number: %" PRIu32 "\n", pass_key);
        /** Inject false if passkeys don't match. */
        NimBLEDevice::injectConfirmPasskey(connInfo, true);
    }

    void onAuthenticationComplete(NimBLEConnInfo& connInfo) override {
        /** Check that encryption was successful, if not we disconnect the client */
        if (!connInfo.isEncrypted()) {
            NimBLEDevice::getServer()->disconnect(connInfo.getConnHandle());
            Serial.printf("Encrypt connection failed - disconnecting client\n");
            return;
        }

        Serial.printf("Secured connection to: %s\n", connInfo.getAddress().toString().c_str());
    }

[goddade]

Is the PIN returned in the onPassKeyDisplay function mandatory?
What is the purpose of calling injectConfirmPasskey in onConfirmPassKey?

[h2zero]

Is the PIN returned in the onPassKeyDisplay function mandatory?

You can ignore this callback and the default passkey will be used.

What is the purpose of calling injectConfirmPasskey in onConfirmPassKey?

It's not meant to be used here in reality, it's just to show what to call to confirm the passkey at some other point in the code.

[goddade]

Is "default passkey" the passkey set in the "setSecurityPasskey" function?

[h2zero]

yes

[goddade]

If I return a different passkey in onPassKeyDisplay, which passkey will be used for verification?

In onConfirmPassKey, the passkey is not verified; it directly calls injectConfirmPasskey(connInfo, true), but I cannot bond using an incorrect passkey.

[h2zero]

If I return a different passkey in onPassKeyDisplay, which passkey will be used for verification?

This will override the default passkey.

In onConfirmPassKey, the passkey is not verified; it directly calls injectConfirmPasskey(connInfo, true), but I cannot bond using an incorrect passkey.

These are 2 different pairing methods, one enters the number on the client and displays on the server onPassKeyDisplay and the other confirms a displayed pin being the same on both devices with a yes/no button.

[goddade]

I don't know much about BLE, thank you for your answer.