Where is the Safest place (blueprint) to store Events that accomplish account checks and validation

Hey fellow humans much love to all,

My understanding is the hierarchy of authority in the blueprints is Instance>Gamemode>Gamestate>Playerstate>Playercontroller>Pawn (AFAIK)
If thats the case the GameInstance would be the place to store how user and passwords get “encrypted” by some homemade “algorithm” then sent out to db server via Run on Server ROC (sent to db by REST api or VaRest plugin in this case)

However from what i understand the GameInstance exists not only on the server, but on the client as well (even though they dont communitcate by ROC due to the instance not being an actor?)
“A separate GameInstance exists on the server and on each client” - Multiplayer in Blueprints | Unreal Engine Documentation

Finally, my question is; does the instance get duplicated to the clients with the nice arrays that i use to “encrypt” the data?
Please correct me and add what you want the more the better :slight_smile:

Update, kind of figured out what RPC actually means! :smiley: