One authentication for multiple characters

Game Design
2

Hello,
I am not sure if I understood your requirement correctly but, you can manually generate deviceIDs and store them in a storage object in the “Main” account while creating;
an example of a stored object:

{
    "server_1": "19fe84a3-0ab0-47f7-b894-34d66e861dc2",
    "server_2": "49f8e91d-4bfe-478c-808a-26e4f19ae860",
    "server_3": "89903ba9-81a7-4015-84b3-9e28df92f0e7"
}

So steps look like this:
Authenticate in the main account (with actual deviceID)
Fetch this stored object, display servers and when the player clicks one of the servers (for example server_2) you grab a manually generated deviceID from that object and re-authenticate using that one.
So you will have multiple accounts with one “main” account.