Flutter – How to differentiate between multiple Firebase Authentication providers (e.g., Apple, Google, Email/Password)?

Some Suggested methods:

Provider-Specific Data in Firebase Authentication:

Firebase Authentication automatically stores provider-specific data in the user object when a user signs up or signs in with different authentication providers. Each provider’s data is included in the providerData array within the user object. You can use this data to identify the authentication method.

Here’s an example in JavaScript:

const user = firebase.auth().currentUser;
if (user) {
  user.providerData.forEach((profile) => {
    console.log('Provider: ' + profile.providerId);
    console.log('User ID: ' + profile.uid);
  });
}

You can then differentiate between providers based on the providerId.

Custom Claims:

Firebase allows you to set custom claims for a user, which can be useful for managing user roles and identifying authentication methods. You can set a custom claim for a user when they sign up or sign in, indicating which authentication method they used.

Example of setting a custom claim in Firebase (JavaScript):

// Set a custom claim to identify the authentication method
admin.auth().setCustomUserClaims(uid, { authenticationMethod: 'google' })
  .then(() => {
    // Claim set successfully
  })
  .catch((error) => {
    console.error('Error setting custom claim:', error);
  });

You can then check the custom claim in your security rules or application logic to differentiate between authentication methods.

Database or Firestore User Profile:

You can create a user profile in Firebase Realtime Database or Firestore that includes information about the user, including their authentication method. When a user signs up or signs in, you can update this profile with the authentication method used.

For example, in Firestore:

// Update the user's profile with authentication method
const userRef = db.collection('users').doc(uid);
userRef.update({ authenticationMethod: 'google' });

This allows you to query and filter users based on their authentication methods.

Custom User Data in Authentication Providers:

Some authentication providers, like Apple Sign-In, allow you to request specific user data during the authentication process. You can use this additional data to identify the authentication method and associate it with the user in your database.

For Apple Sign-In, you can request the user object, which includes information like the user_id and identityToken. You can store this information in your database.