Best Auth for a Mobile App: Clerk, Supabase Auth or Firebase

If you are building a mobile app and want one name, pick Firebase Authentication. If your data already lives in Postgres and you want row-level security tied to the signed-in user, pick Supabase Auth. Pick Clerk only when the same accounts also power a web dashboard and you want its prebuilt screens and organizations.

That ordering is different from what we tell web founders. Our Auth0, Clerk and Firebase Auth comparison leans toward Clerk because most of the pain on the web is framework glue. On a phone the pain is somewhere else. It is the Apple review, the redirect that lands back in the wrong app state, the token that has to survive a force quit, and a user standing in an elevator with no signal.

The rest of this post goes through those mobile problems one at a time. Prices and limits below are what we saw published in 2026. Every vendor has changed its free tier at least once in the last two years, so check the pricing page on the day you sign up.

Apple's App Store rules say that if your app offers a third-party or social login such as Google or Facebook, you generally have to offer Sign in with Apple too, or another login service that meets Apple's privacy requirements. There are narrow exceptions, for example apps that only use your own account system. Read the current guideline before you build, because reviewers do enforce it and a rejection costs you days.

All three providers support Apple as a sign-in method. The difference is how much work it takes on a phone.

Firebase

Firebase has the most mature native path. On iOS you run Apple's own authorization flow, get an identity token, and hand it to Firebase as a credential. React Native has community and official wrappers for the same flow. It works, and it is the path with the most blog posts, Stack Overflow answers and sample repos behind it.

Supabase

Supabase supports Apple through an ID token exchange. You get the token from the native Apple sheet and pass it to the auth client. That is the right way to do it on mobile, because the browser-based OAuth route feels wrong inside an app. Expect to configure the Apple service ID, key and bundle ID in the dashboard by hand.

Clerk

Clerk offers a native Apple flow in its Expo and React Native tooling, and the prebuilt pieces cut the setup down. The catch is that some of the native flows need a development build rather than Expo Go. That is normal for anything touching native modules, but plan for it.

One Apple detail catches everyone. Apple only gives you the user's name and email on the very first authorization, and the email may be a private relay address. Whichever provider you use, save the name the first time or you will not get it again. Also remember that if your app lets people create an account, it must let them delete it from inside the app. Check how each provider deletes a user and wire that to a button early.

A mobile session is a refresh token sitting on a device you do not control. Where it sits matters more than which vendor issued it.

The right place is the iOS Keychain and the Android Keystore. Not plain app storage, not a JSON file, and not the default key-value store that many React Native tutorials use because it is easy. That default store is not encrypted. On a rooted or jailbroken phone, or in an unencrypted backup, a refresh token stored there is readable.

What each one does by default

• Firebase native SDKs persist the signed-in user in the Keychain on iOS and in app-private storage on Android. You do almost nothing. In React Native with the web-style JS SDK you have to choose a persistence layer yourself.
• Supabase in JavaScript takes a storage adapter. The docs examples often show the plain async key-value store, and you should swap it for an encrypted one backed by Keychain and Keystore. In Swift, the client stores the session in the Keychain by default.
• Clerk in Expo asks you to pass a token cache, and its docs point you to the Expo secure store, which wraps Keychain and Keystore. Good default, but it is a step you have to remember.

One limit to know about. Secure store on some Android versions has size limits for a single value, so stuffing a whole large session object into one entry can fail. Store the tokens, not the whole user profile.

Also decide what happens on a fresh install. iOS can keep Keychain items after the app is deleted and reinstalled. That surprises people when a user reinstalls and is still signed in, or when you sign someone out on the server and the device still holds a stale token. Clear your stored session on first launch after install if that matters for your product.

Social login on a phone means leaving your app, signing in somewhere else, and coming back through a URL. This is where most of the real bugs live, and no vendor hides all of it.

Use a proper redirect that the operating system hands to your app. Universal Links on iOS and App Links on Android are the safe choice. A custom URL scheme works but any other app can register the same one, which is a real phishing risk. Use the system browser session meant for auth, the in-app browser sheets that share cookies with Safari or Chrome, rather than a bare web view. Google blocks OAuth in embedded web views, and Apple's guidance does not like them either.

Where each provider helps

Supabase leaves the redirect handling to you, and the Expo guides walk through reading the returned URL and setting the session. That is clear once you have done it once and annoying the first time. Clerk wraps this in its hooks, so you write less. Firebase sidesteps most of it for Google and Apple on native, because the native SDKs return a credential directly instead of bouncing through a browser redirect.

Magic links and email confirmation share the same problem. The link in the email must open your app, not a mobile browser tab showing a spinner. Test on a real phone with the app installed and with the app not installed, because the second case is what a new user sees. Set a web fallback page that tells them what to do.

A test we run on every build: sign in, kill the app mid-redirect, reopen, and check that the user lands on a sensible screen and not a blank one.

Passkeys are the best sign-in experience a phone can offer: tap, Face ID, done. No password to forget, nothing to phish. We cover the standard in the passkeys and WebAuthn guide, so here is only the mobile question: which provider gets you there with the least work.

Support is uneven and it changes quickly, so verify against current docs before you commit. As of our 2026 check, Clerk lists passkeys as a supported sign-in method and has been working on native mobile support. Supabase has not shipped a first-party passkey sign-in as far as we found, and teams who want one tend to pair it with a custom flow or a separate service. Firebase Authentication has no built-in passkey method that we could confirm, so most teams add a server component that verifies the WebAuthn response and then mints a Firebase custom token.

That sounds like Clerk wins. For a pure passkey requirement, it may. But do not confuse passkeys with Face ID or fingerprint login. Many apps only need Face ID or fingerprint to open a session that already exists. That is a local check against the Keychain item, and it works with any of the three. The two are different features with different risks.

My advice is to ship email or social login with Face ID or fingerprint re-entry first. Add passkeys when users ask or when support tickets about lost passwords start to pile up. Passkeys need a domain you control, an association file served from your site, and a recovery story for people who lose their phone. That is a week of careful work, not an afternoon.

Phones lose signal. A good mobile auth setup keeps the user signed in with no network, and refreshes tokens quietly when the network returns.

Access tokens are short lived, often an hour. Refresh tokens last much longer. Your app should open straight into cached content, show the user as signed in, and refresh in the background. The mistake we see is a splash screen that waits on a network call to confirm the session. On a train that means a spinner and then a logged-out screen, and a one-star review.

How the three behave

• Firebase native SDKs keep the user object locally and refresh the ID token on demand. If the device is offline, the user stays signed in and calls to your own backend fail until you reconnect.
• Supabase auto-refreshes by timer in the client. In React Native you must tell it when the app moves to the foreground or background, or the timer misbehaves while the app is suspended. The docs show the small app-state listener to add. Forget it and users get signed out for no visible reason.
• Clerk keeps a session token that it refreshes frequently and keeps in the cache you gave it. Its model leans on talking to Clerk often, so a long stretch offline followed by a cold start deserves a test on your side.

Whatever you pick, define what the app does when the refresh fails because the refresh token was revoked, versus because there is no network. Those are two different cases. Revoked means sign out. No network means stay in and retry.

Marketing pages list "mobile support". What you care about is which SDKs exist for your stack and how often they break when iOS or Expo ships an update.

Firebase

The strongest mobile story of the three. Maintained native SDKs for iOS, Android and Flutter, plus solid React Native bindings. It is also a Google product with a long history of keeping these libraries current. The downside is the sprawl of choices. There are two or three ways to do the same thing in React Native, and the docs do not always tell you which is current.

Supabase

A good JavaScript client that works in Expo and React Native, and an official Swift client and Kotlin client, which means native iOS teams are covered. The sharp edge is the storage adapter and app-state handling I described above. Once configured it is stable. The real draw is that the signed-in user's id flows into Postgres policies, so your mobile client can query data directly and the database enforces who sees what. For a deeper look at the database side, see our Supabase vs Firebase comparison.

Clerk

Clerk's Expo SDK is aimed at React Native developers, with hooks and prebuilt components. It is the quickest route to a polished sign-in screen if you are on Expo. I would be more careful if you are writing a fully native Swift or Kotlin app, because Clerk's center of gravity is JavaScript. It does offer native SDKs, but they are younger, so read their current release notes and issue tracker before betting a launch on them.

If your team writes native Swift, Firebase or Supabase give you the least friction. If your team writes Expo and TypeScript, all three work and the choice moves to pricing and what else you need.

Mobile apps tend to have a lot of free users and few paying ones, so the unit price matters more than the monthly fee. These are ranges from public pricing pages and write-ups we checked in 2026. Treat them as a guide and confirm on the vendor page.

Firebase Authentication

Email, social and anonymous sign-in sit in a generous free tier, commonly reported at around 50,000 monthly active users on the upgraded Identity Platform plan, with per-user rates beyond that in the fractions of a cent. The line item people forget is SMS. Phone number sign-in is billed per message and the price changes a lot by country, from a cent or so in the US up to tens of cents in expensive regions. SAML and OIDC federation is priced in a separate tier at a higher per-user rate.

Supabase Auth

The free plan has been reported at about 50,000 monthly active users for auth, and the paid plan at about $25 a month with roughly 100,000 included and a fraction of a cent per user after. You are also paying for a database in the same bill, so compare the whole project, not only auth. Free projects can pause after a period of inactivity, which is fine for a prototype and a problem for a live app.

Clerk

Clerk changed its pricing in early 2026. Its own material describes a free plan in the tens of thousands of users, counted as monthly retained users instead of monthly active users, with a paid plan from about $25 a month and roughly two cents per user beyond the included amount. Third-party sites still quote the older 10,000 figure, so read the current page. Per user, Clerk costs several times more than Supabase once you pass the free tier.

For a consumer app with a million free users, that gap is thousands of dollars a month. For a B2B app with five thousand paying seats, it barely registers. Do the arithmetic with your own user count before you decide. If you are budgeting the whole build, our app development cost page and the guide to building a SaaS platform show where auth sits next to everything else.

Here are the situations we see most, with a pick for each.

A consumer app on Expo with a simple backend

Firebase Authentication. Free at scale for email and social, native sign-in flows, and the biggest pile of working examples. Watch the SMS bill if you use phone login.

A native Swift or Kotlin app

Firebase or Supabase. Both ship maintained native clients. Pick Supabase if you want Postgres, and Firebase if you want the rest of Google's mobile tooling.

An app where the database is the product

Supabase Auth. Row-level security tied to the signed-in user means fewer API endpoints to write and fewer places to forget a permission check.

A mobile app plus a web dashboard, with teams or organizations

Clerk. One user model across both, prebuilt screens, and organizations without building invitations yourself. Accept the higher per-user price.

Passkeys on day one

Clerk, if its current native support covers your platform. Otherwise plan the extra server work on Firebase or Supabase.

A heavily regulated or enterprise-first product

None of these three by default. Look at Auth0 or a similar enterprise vendor, and start with our Auth0, Clerk and Firebase comparison.

Whatever you choose, keep your own user id in your database and treat the provider id as a field, not the key. That one decision makes a later switch a weekend of work instead of a quarter. Kanopy helps founders pick a stack and build the product on it, so if you want a second opinion on yours, Book a free strategy call.