When you log in to Firebase (or any application) using Gmail and then attempt to log in with Facebook using the same Gmail address, you end up with two different accounts due to how the identity providers and authentication processes work. Here’s a detailed explanation of why this happens:
- Different Identity Providers
When you use Gmail to log in, you are authenticating against Google's identity provider. When you log in with Facebook, you authenticate against Facebook's identity provider. Each service has its own way of managing users and their authentication. While both accounts may use the same email address, they are still managed by different providers, leading to the creation of separate accounts in the Firebase application.
- Distinct User Entries in Firebase
In Firebase Authentication, each user is represented by a unique user ID (UID) tied to a specific authentication method. When you log in with Gmail, Firebase creates a user record associated with your Google account and generates a unique UID for that user. When you switch to Facebook login, Firebase treats this as a completely different authentication method, resulting in the creation of a new user record linked to your Facebook account, even though both accounts share the same email.
- Lack of Account Linking
To unify logins, the application must specifically implement an account linking feature. Firebase provides the ability to link accounts, allowing you to connect different sign-in methods (for example, linking a Google account with a Facebook account). However, if this feature is not used or configured properly, users will end up with separate accounts for each login method, even when using the same email address.
4.User Experience Design
From a user experience perspective, this design forces users to manage accounts separately when using different OAuth providers. It can potentially prevent unauthorized access if one provider is compromised, contributing to the overall security of the user’s identity.
Conclusion
To resolve the situation where a user wants to access a single account regardless of the login method (Facebook or Google), they can link accounts. This would allow you to sign in with either method while retaining access to the same user profile and data in the application. If you encounter this situation, consider checking the application’s settings for an account linking feature that integrates both methods under one user profile.
