MQTT Authentification in Asp .Net Core 3.1

Hello can anyone advise how to implement Authentification(username and password FROM DB level) in MQTT platform, currently have few ideas in mind:

1. Authenticate on every message received from client, problem is database would get huge load just for checking if many users are provide valid login data.

2. Implement other authentication solution(JWT?), then how to implement in current solution(link to github)

There are two projects one Asp .Net core MQTT "server" and other .Net Core Console App "client"

Github link to plain MQTT implementation(Mosquitto config also included if anyone needs it)

Github

Thanks for help.