The Role of Authentication Tokens 1. The Role of Authentication Tokens Each provider generates a unique authentication token. Firebase uses this token to create or identify an account. If a user logs in with Facebook, Firebase creates an account based on this token, without checking if an account with the same email address already exists through another provider. 2. Risk of Account Duplicate Without explicit management, Firebase can create multiple accounts for the same person. This leads to duplicates in the database, separate sessions, and fragmented user data. The user may believe they are logged into their usual account, when in fact it is a new profile. 3. The `auth/account-exists-with-different-credential` Error If Firebase detects that an account already exists with another provider for the same email address, it may return this error. However, this only occurs if the email address is correctly shared and recognized. Otherwise, Firebase creates a new account without warning.