Best auth providers for AI-built apps

Best auth providers for AI-built apps

No single auth provider is best for everyone. Auth0 suits teams needing a standalone identity provider. Clerk suits teams wanting hosted auth components separate from their database. Firebase Authentication suits apps already on Firebase or Google Cloud. Supabase Auth suits projects already on Supabase that want auth and database access rules in one system. The list is alphabetical and is not a ranking.

How we picked and ordered these

This covers the databases, backend platforms and sign-in services that AI app builders wire up. We only feature a tool when a page owned by the vendor backs our description of it.

We do not rank them. Each entry says what the sources report, where it falls short, and who it suits, so you can match one to your own situation. Where a competitor of ours is the better fit, we say so.

We read each source on 2026-11-05. Prices and limits change often, so confirm on the vendor's own page before you buy. A figure marked "one source only" was not matched by a second publisher.

At a glance

The auth providers, one by one

Auth0

Auth0 is an identity platform with a Free plan and paid Essentials and Professional plans whose price scales with monthly active users.^[1]

Limits and things to check:

• Auth0's FAQ states that beyond 25,000 users a paid plan is needed.^[1]
• Auth0's pricing page lists custom tiers for Essentials and Professional external active users.^[1]
• G2 lists separate B2B plans at $150 per month (Essentials) and $800 per month (Professional).^[6] One source only.

Pricing as reported for Auth0:

• Free: $0 (Up to 25,000 monthly active users) ^[1]
• Essentials: $35 per month (Most sources say up to 500 MAU; G2 lists up to 5,000 MAU. Disagreement) ^[6] One source only, so confirm it on the vendor page.
• Professional: $240 per month (Most sources say 500 MAU; G2 says up to 1,000 MAU. Disagreement) ^[6] One source only, so confirm it on the vendor page.

Suits teams needing a standalone identity provider. That is our reading of the facts above, not something a source says.

Clerk

Clerk provides hosted user authentication and management with Hobby, Pro, Business and Enterprise tiers.^[2]

Limits and things to check:

• Clerk's updated pricing post (older) announced 10,000 MAUs free and a new Pro plan.^[7] One source only.
• Search summaries describe overage at about $0.02 per additional user above the allowance.^[2]
• 2026 third-party sources describe the free allowance as 50,000 monthly retained users rather than MAUs, conflicting with the 10,000 MAU figure.^[8] One source only.

Pricing as reported for Clerk:

• Hobby: $0 ^[7] One source only, so confirm it on the vendor page.
• Pro: $25 per month ($20 per month billed annually per one third-party source; overage about $0.02 per additional user) ^[2]

Plan limits are longer than fit here and some sources disagree on them, so read the limits on the vendor pricing page.

Suits teams wanting hosted auth components separate from their database. That is our reading of the facts above, not something a source says.

Firebase Authentication

Firebase Authentication is billed through Google Identity Platform, which is no cost up to 50,000 monthly active users.^[3]

Limits and things to check:

• Google's Identity Platform pricing page says it is no-cost up to 50K MAUs.^[3]
• Phone and multi-factor authentication are charged per message with a region-specific rate table.^[3]
• SMS rate sources conflict: one puts US and Canada at $0.01 per SMS, another cites $0.04 in us-central1.^[9] One source only.

Pricing as reported for Firebase Authentication:

• Identity Platform: $0 up to 50,000 MAU (SAML/OIDC allowance is 50 MAUs; phone and multi-factor users are charged per message sent, with the first ten SMS per day free) ^[3]

Suits apps already on Firebase or Google Cloud. That is our reading of the facts above, not something a source says.

Supabase Auth

Supabase Auth issues JSON Web Tokens that scope database access row by row when used with Row Level Security policies.^[10]

What the sources say:

• Users can sign in with password, magic link, one-time password, social login and single sign-on.^[10]
• Auth uses JSON Web Tokens, and the token scopes database access on a row-by-row level when used with RLS policies.^[10]
• Any OAuth2 or OIDC-compatible identity provider can be added through custom OAuth/OIDC providers.^[10]

Limits and things to check:

• Supabase docs state that charges apply to Monthly Active Users, Monthly Active Third-Party Users, Monthly Active SSO Users and Advanced MFA add-ons.^[10]

Pricing as reported for Supabase Auth:

• Included with Supabase Free: $0 (50,000 monthly active users per third-party summaries) ^[11] One source only, so confirm it on the vendor page.
• Included with Supabase Pro: $25 per month (100,000 monthly active users included; overage $0.00325 per MAU per vendor pricing page as summarised in search) ^[4]

Suits projects already on Supabase that want auth and database access rules in one system. That is our reading of the facts above, not something a source says.

How to choose a auth provider

Start from your situation, not from the list:

• For teams needing a standalone identity provider, start with Auth0.
• For teams wanting hosted auth components separate from their database, start with Clerk.
• For apps already on Firebase or Google Cloud, start with Firebase Authentication.
• For projects already on Supabase that want auth and database access rules in one system, start with Supabase Auth.

Open the vendor pricing page for your shortlist before you decide, since plans change.

Where Continuum fits

We make Continuum Supabase Security Review. Weigh what we say here with that in mind. The tools above are the better choice when you want software you run yourself; ours is the better choice when you want a person to do or read the work.

Continuum Supabase Security Review (ours)

A human review of a Supabase app covering row level security policies, key exposure, storage rules, auth config and service-role usage.^[5]

What our own page says:

• It returns ranked findings with corrected SQL and a proof for each, in 48 hours.^[5]

Limits and things to check:

• It is a manual review of one app, not a continuous monitor.^[5]

Pricing as reported for Continuum Supabase Security Review:

• Supabase Security Review: Quoted on the page (48 hour turnaround) ^[5]

Suits a team running on Supabase that wants a person to read its policies and keys before launch.

Details on Continuum Supabase Security Review.

Running on Supabase?

Straight answers