Zero Trust Tunnel with GitLab Mattermost

Hello everyone,

i have a self-hosted instance of GitLab (Community Edition) that is accessed using a Zero Trust. I also would like to use GitLab’s Mattermost.
But the issue is, Mattermost works with Port 80, just like GitLab. But GitLab internally routes Requests to the Mattermost Domain to the correct Service.

Now my question is, has anyone tried this before? Does anyone have suggestions on how to solve this?

Does cloudflared forward the original Domain to the Target?