Is there any way to use username&password to connect AWS IoT without ALPN tag?

Per my info, connecting to AWS IoT using mqtts:// (TLS, port 443) without setting the ALPN tag is not directly possible. The ALPN tag is crucial for the server to identify the protocol being used, and without it, the connection attempt will likely fail.

Maybe use port 8883 - This is the standard port for MQTT over TLS with client certificate authentication in AWS IoT. You can connect to your IoT endpoint using mqtts://<endpoint>.iot.<region>.amazonaws.com:8883 and provide your device certificate and private key during the connection process. I don't think ALPN tag will be needed in tht case.

If you need to use port 443 specifically, you can create a custom authorization policy that uses a Lambda function to validate the username and password. This approach requires more configuration but allows you to connect using username and password on port 443.Configure your MQTT client to connect to the endpoint using mqtts://<endpoint>.iot.<region>.amazonaws.com:443 and set the ALPN tag to "mqtt".