How to run Dedicated server on Steam? is it allowed?

For example if i use FOnlineSubsystemSteam and will make game for Steam, how to handle Server logic? how to check incoming Client data on server side?

Should i make my own OnlineSubsystem and Online service for that?

Is there any UE4 OnlineService interface for creating server-side Pair for OnlineSubsystem?

Or how to provide Steam master server with information about my dedicated server? or what?