Hi Dojo,
I'm creating a flow in Power Automate that when a maintenance window is scheduled it will send a Teams message to every person that is logged in on my system.
For this I'll make us of Webhooks to retrieve a JSON list of logged in persons. But which call can I use to have the persons that are currently logged in?
We were recently asked to provide something similar and a workable solution would be to use the information events. Every time a user logs in/out of DataMiner an associated information event is logged.
Depending on the application (Cube, HTML5 Apps) used you could see various messages (e.g., New Client Registered). You can then write a simple automation that retrieves the clients that have logged in but not logged out yet and notify those. 
Hope it helps.