I’m currently using monero addresses as the sole authentication method for a custodial service, similar to how mullvad VPN has a single account number to authenticate. My understanding is that these are unique, and impossible to guess. For a custodial service, this makes withdrawing user funds trivial as well.
Can anyone tell me why this is a bad idea?
Its a good idea.
If the service supports delegated user accounts (some permissions but not full account access), it might not work