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Anonymous First, Passwordless Second Firebase Authentication - November 23, 2020

Delivering delightful and persistent experiences without requiring immediate authentication is a pleasant shift in todays world of applications. It is empowering to allow someone the freedom to try out an application before they sign up for everything that authentication mechanisms enable behind the scenes. This post explores one alternative solution to the authentication experience.

Before Diving In

This post leverages Firebase to demonstrate the concept of anonymous first, passwordless authentication. I will aim to target 2 powerful features that empower developers to integrate Anonymous Users and Passwordless Authentication. They can be used exclusively, but together they work quite nicely.

Even though this post carries iOS specific undertones, the underlining flow is adaptable for any Firebase driven client application and can be extended as a general authentication practice for a wide variety of applications not backed by Firebase.


There are many ways to provide application users with persistent, attributed, and social experiences. Many applications implement some form of a user session, perhaps with accounts and authentication. Social media logins have become more or less a standard and for good reasons. As a user I don’t need to worry about maintaining a specific password for many of my apps and as a developer I don’t need to worry about managing a user table and correctly handling passwords.

There is even more value in user association in applications.

However, it feels like most applications I download present me with a social based “authentication wall” before I am even allowed to play around.

This brings up the question; why do we force authentication before giving people the chance to get a feel for their newly downloaded application?

It is worth thinking about what user data an application truly needs.

If you answered yes or no to any of those you might want to think about anonymous users.

It is easy to jump to social login first thing in an application because at the end of the day applications are supposed to benefit users and be as personalized as possible.

But what if we changed this default? What if applications empowered users to opt-in instead of being forced-in to authentication? Just like the user had the decision to download the application, shouldn’t they be permitted the decision of not logging in if they don’t want to?

Why not try out an anonymous first flow?


Setting up a firebase application with anonymous users is outlined in Firebase documentation under your specific platform’s Anonymous Authentication tab. Once the SDK is installed and configured to your firebase instance you’re ready to begin the flow.

About Anonymous Users

Treat an anonymous account just like any other authenticated account, they’re just not linked with a social provider and you don’t have any specific user information like email off the start of the users life. Each anonymous user has their own UID and that can be linked and referenced accordingly.

This concept allows us to give user experiences tailored to their active sessions, persisted to a backend, and permit a less invasive, opt-in approach for authentication.

A caveat: Firebase Anonymous users don’t expire and there isn’t currently any automated way to remove them. This brings up the importance of correctly linking and removing anonymous users during the time when users opt in to explicit authentication or when they sign out.

The Flow

There truly isn’t too much addition to a traditional authentication flow when adding Anonymous First users. As the application launches, the firebase application is configured and a check to see if there is a current user session occurs by supplying the authentication state listener. In iOS world, by assigning the addStateDidChangeListener we can receive state updates about the active user. If the User object comes back nil we can go ahead and proceed to the No User case below.

No User

If there is no user session we jump straight in to creating an anonymous user! The Authentication package from firebase allows us to make a single call signInAnonymously() and we are off and running with an anonymous user.

Anonymous User

If there is a user then Firebase Users have a property isAnonymous which will be able to tell us if that user is anonymous.

Authenticated User

Otherwise we have an authenticated user and we can bypass the previous two steps.

Anonymous or not, once we have a User, we can treat them the same. There will be a unique identifier in Firebase’s Authentication tab for whoever is using the application.

How to handle when a user wants to opt-in to Authentication

There are a few things to keep in mind when a user decides they want to authenticate with your application.

  1. User signs in to an account that has never been in your system before. This case is incredibly simple thanks to account linking. Linking allows us to take the UID from the anonymous user and assign a “link” to the social provider that we are signing in with. Essentially the anonymous user “evolves” into this new authenticated user for free.
  2. User signs in to an account that already exists. In this case the linking step from above won’t be as simple. We need to signIn as the new user while keeping a reference to the previous anonymous user. When the new user is successfully signed in we need to take this time to re-associate the previous users assets to this existing user’s UID. Once that is complete we can then delete the anonymous user as it will no longer be needed.

Passwordless sign in

Once a user is ready to take their account to the next level and link an email address and perhaps other personal information, we can use a social provider strategy (Google Auth/Apple Auth). OR we can use a an email link authentication approach! This way we can link a users email address without them needing a password and without requiring them to belong to a social provider.

The specific passwordless mechanism used by firebase is called Email Link Auth and they are handled through mobile applications as universal links from an email generated by firebase.

This sign in requires us to set up Firebase Dynamic Links.

Passwordless authentication is a beautiful way to gain user attribution without requiring anyone to carry a social media account. This could reduce the requirement of sign in supports as well since Apple now requires Apple Sign In if your iOS app uses almost any other social sign in provider.

On top of all that, no more reused or remembering passwords by the user, besides their email.

Common Firebase Error states

There are A LOT of errors to potentially account for when dealing with Firebase Authentication. However there are a few common errors I’ve seen regularly that are nice to know ahead of time.

Signing out

When a user signs out of an authenticated user make the choice to either save some data or completely wipe local data when returning them back to an anonymous state. When the signOut callback is successful we find ourselves back in the “No User” state and should create a brand new anonymous user ready for action.

It is a nice clean up step to remove the previous anonymous user at this step, as there will not really be a way for a user to associate themselves with that anonymous user again.

Signing out of an anonymous user is not an option I would personally suggest presenting to a user unless you inform them that it will “reset” them.

That’s it

Anonymous First, Passwordless authentication may not be the correct solution for your application. Keeping this option in the back of our toolbox can potentially improve user adoption and increase awareness for something that has taken time and energy to create.

I present this flow with experience from Firebase. If Firebase is not your cup of tea or your project does not use Firebase, you can still use similar principles to the flow pattern to deliver a pleasant user experience in your applications.

Last but not least, if you would like to see this idea in action, I’ve built out an isolated application to illustrate the flow. Feel free to check it out here, you’ll need to add your own Google Service Plist.