VerneMQ supports enhanced authentication flows or SASL style authentication for MQTT 5.0 sessions. The enhanced authentication mechanism can be used for initial authentication when the client connects or to re-authenticate clients at a later point.
The on_auth_m5 hook allows the plugin to implement SASL style authentication flows by either accepting, rejecting (disconnecting the client) or continue the flow. The on_auth_m5 hook is specified in the Erlang behaviour on_auth_m5_hook in the vernemq_dev repo.