The authentication system using Mattermost is quite simple. Just provide the email address and the password you had used to register at Mattermost, and you will get authenticated!
Important note
Mattermost based community is now deprecated. Our server got overloaded, and we have moved to the free Discord based teamTAD community. Explained here We will be shutting down the Mattermost based chat community on October 31, 2020. If you have a registration at our older Mattermost community, we strongly urge you to move your membership to the new Discord based teamTAD community. Use this invitation link: https://tiny.cc/ttad
Also important: Read what you need to do when migrating to the Discord teamTAD community