STRIX itself doesn’t have a user management feature in it, but it can use an external user management system.
If we can assume that the client has authenticated a user and that only the identification of users is needed, you can set the user’s identity in the room member property called "name". If your title distinguishes a user name to be shown to players and a user ID to be used internally by programs, you usually store the user name in the "name" property and the user ID in a custom property that you define. The convention is to use "userId" as the name of the custom property for your purpose.
If you want the server to receive an authenticated user information, a token authentication scheme is available. That is, you run an external authentication server to issue an authentication token, the client passes it to the STRIX server, and the STRIX server gets the user name and user ID from the authentication server. Under this scheme, the user name and the user ID that the STRIX server gets from the authentication server are automatically set to the "name" room member property and the "userId" custom room member property, respectively.
Please refer to the Strix Unreal SDK User’s Guide for details about the token authentication scheme. Please refer to the Strix Cloud User’s Guide on how to set up your servers to perform the token authentication in Strix Cloud.