Private metadata on mobile notifications
My organization is using Mattermost heavily, and we'd like to receive mobile notifications to make it more useful. However, currently Mattermost shares a lot of metadata with Apple's and Google's servers:
This is preventing us from enabling notifications.
I'd like to suggest that you treat the Apple and Google push notification services just as a "wake up" signal, without including user ID, team ID, etc. The mobile app would then connect (via TLS) to its server, download any new messages, and generate local notifications based on those.
I recently spoke with someone on the Mattermost team who suggested that push notifications on iOS cannot wake the app, but this information is out of date. Current best practice on iOS is PushKit (https://developer.apple.com/documentation/pushkit), which can wake apps.
Numeric IDs are not sensitive data, you cannot do anything useful with them. However, human-readable team/channel/user names or even message contents are a problem. Disabling them in the settings is not great, because e.g. on smartwatches this makes notifications basically useless.
Unfortunately Mattermost is not "privacy-first" in this regard, as their new "ID-loaded notifications" feature (which is exactly what you are asking for) is restricted to Enterprise Edition E20, even though this would be good for privacy even on a small Team Edition instance!
Other messaging apps like Threema are also doing this in the same way (wake up only, retrieval of message with the triggered app). This way, no private information is available on the push servers while still the contents of the message can be displayed in notifications (and also on devices like a smart watch). This would really be a great feature. Right now, we also turned off message contents in push message as otherwise all company internal messages would again be available at some third party location.
There's also the possibility of using the mutable-content feature for this: https://developer.apple.com/documentation/usernotifications/modifying_content_in_newly_delivered_notifications#2942066.