Firebase: Standard User Registration/Activation Workflow

Question

I need to implement a standard user registration/activation workflow with Firebase. There doesn't seem to be an obvious way to implement this. When I say "standard", I mean how most email/password accounts work - not necessarily specific to Firebase. I'm sure you're familiar with this. This is the workflow:

• User enters their username/password on a form with some validation and submits details
• The back-end creates the user record in the database, but the account remains deactivated (i.e. user cannot authenticate - the activated flag is set to false)
• The back-end sends an email to the user with a link to activate the account
• The user clicks the link in their email which triggers activation. This is probably a Web API of some description.
• At this point, the user record's activated flag ticks over to true, and the user can now authenticate
• The link probably also has a deep link that opens the app or navigates to a web page
• The user can now log into the app

How do I configure Firebase to do all this?

Currently, the app allows the user to register. I am using the Flutterfire SDK. I call createUserWithEmailAndPassword, which successfully creates the user in Firebase. But, the user is already activated. The user should have a state of "disabled" in firebase until the account becomes activated. I can't find any settings to default the user to disabled when the account is first created.

I also managed to get Firebase to send out an activation email by calling sendSignInLinkToEmail, but this call is really designed for email authentication - not email activation. Opening the link should activate the account, but I have not figured out how to do this. This documentation makes it sound like it is possible. Perhaps, the Flutterfire SDK is missing this? I don't want to allow people to log in without a password. I only want to use this call to send out an email.

What am I missing here? Is this non-standard behavior for Firebase? If so, why? If the user is allowed to use an app with an email address that is not activated, they can impersonate someone else. We need to confirm at least that they are custodians of the email address that they are claiming to have.

Do other Firebase people just not worry about this?

Lastly, I know I can achieve this by creating a collection for users in Firebase and putting an "activated" flag there. But, if I do that, I've got to write a cloud function that accepts the link and then updates the user in the collection based on the received link. But I thought this would be automatic in Firebase. If Firebase doesn't have this built-in, I have to put all the security over the top to stop users from authenticating when they have not yet activated their account.

Answer 1

This is a pretty valid concern. I suppose the way around this is to check whether the signed-in user is verified whenever the app is launched. The User object that is returned from Firebase Auth has an emailVerified flag. Check this page for more details.

Using this flag you can choose to show a different screen or pop-up that has a button to send a verification link to the registered email address. Until the user verifies this address, you can limit access to some of the app's screens if you want.

Please note that I have not checked if this emailVerified flag is true for sign ups using Federated login providers like Google Sign-in and Apple Sign In. You might want to check that out.