Hi @jurgenhaas,
I can understand the desire to be able to comment straight from Mattermost to GitLab, that would be pretty cool. Unfortunately it looks to resolve those two issues I think you'd need a more rich integration between GitLab and Mattermost.
- This is the hardest issue to solve, and to do properly we'd need to build the GitLab integration directly into the Mattermost codebase and it would then have access to post as a GitLab user through OAuth2. The best solution besides doing that is to just post as a bot and have the bot start the message with who made the post in Mattermost.
- You might be able to get around this using a bot that acts as an intermediate between Mattermost and GitLab. It could add and remove keywords from the message (or possibly some other field) to identify which messages need to be posted or which would be duplicates.
- Another issue is having the bot determine which GitLab issue to post to based on the post from Mattermost. I'm not sure how you'd handle this with the webhooks as they are right now without having your users manually add some information to the post in Mattermost, which isn't a particularly good solution.