As the title states, is there any way to see what user is currently logged in from the plug-in?
If not, there should be!
Going past that, there should be a way to see what content restrictions (movie and TV ratings) there are on the currently logged in user, if there isn’t already.
Plex channel plugins are just requesting data from a remote server and then allowing you to use that data to display and play content. Data that you want to save and use in multiple sessions can be stored locally in preferences or a dictionary file. Preferences are used to store log-in data and can be pulled and sent as part of data request of a remote server.
But any data about users that are logged into a remote server would need to be requested from that remote server. The remote server you are accessing would have to provide a method of requesting any data about users of that server and their restrictions for use of that server.
So, if you are wanting to access user data from a local Plex Media Server, that would be part of the Plex web API, not the channel API.