Hi,
I have initiated a project to allow LDAP authentication on Mattermost Team Edition, without using Gitlab. This module uses a Oauth PHP server to link LDAP to Mattermost.
If you are interested by the project you can download it from my Github repo : https://github.com/Crivaledaz/Mattermost-LDAP
I have implemented this module for my company to use LDAP with Mattermost and we have been using it for a few weeks. I will be happy to answer your questions about this module. Please do not hesitate to give me your feedbacks.
Regards,
Crivaledaz