Using PlayFabClientAPI.LoginWithCustomID I can get the playfabid in the client, how can I do the same with the server api (java). I have a custom server and a database with users, I'm using the user id as a custom id for the login with playfab so since I already have the custom id in the server I don't want to rely on the client to get the playfabid. Tried PlayFabServerAPI.LoginWithServerCustomId but it seems to have another purpose.