There is no direct mapping from LoRaWAN to MQTT that can be used in a multitenancy environment.It probably will not be created either because of the bandwidth, message size and duty cycle limitations in LoRaWAN. I guess your best bet is to arrange the mapping from nodes to tennants within your application. You might want to read this document or this one to get an idea about the architecture.
Note that TTN is about LoRaWAN which uses LoRa modulation.