Auth Provider Comparison

Choosing an auth provider is one of the highest-leverage decisions in a project's lifetime. The wrong choice costs months of migration work. The right choice eliminates an entire category of security vulnerabilities. This page provides a rigorous comparison of every major auth provider, a build-vs-buy decision framework, and migration strategies for when you inevitably need to switch.

Build vs Buy Decision Framework

When to Buy (Use a Provider)

Signal	Why
Team size < 20 engineers	You cannot afford a dedicated auth engineer
Time to market < 6 months	Building auth from scratch takes 3-6 months for production quality
B2B SaaS needing enterprise SSO	SAML/SCIM implementation alone takes 2-4 months
Compliance requirements (SOC 2, HIPAA)	Providers come pre-certified
No security team	Auth bugs become breaches without dedicated security review
Multiple client types (web, mobile, API)	Providers handle all SDK variations

When to Build

Signal	Why
Auth IS the product (identity platform)	You need full control of the auth experience
Extreme scale (100M+ users)	Provider pricing becomes prohibitive
Unusual auth requirements	Custom MFA flows, hardware token protocols, edge cases
Regulatory requirements forbid third-party data processing	PCI DSS Level 1, classified systems
Strong internal auth team (3+ engineers)	You can maintain and audit the system
Latency-critical (< 50ms auth decisions)	Provider round-trips add latency

The Hybrid Approach

Many production systems use a provider for the heavy lifting (SSO, MFA, user management) but keep critical auth decisions in-house (authorization, session management, rate limiting).

Feature Comparison Matrix

Core Authentication Features

Feature	Auth0	Clerk	Supabase Auth	Firebase Auth	Keycloak	FusionAuth
Email/password	Yes	Yes	Yes	Yes	Yes	Yes
Social login	50+ providers	20+ providers	Google, GitHub, Apple, etc.	Google, Facebook, Apple, etc.	Configurable	30+ providers
Magic links	Yes	Yes	Yes	Yes (email link)	Plugin	Yes
Passkeys/WebAuthn	Yes	Yes	Community plugin	No (planned)	Plugin	Yes
TOTP MFA	Yes	Yes	Yes (v2.55+)	No (phone only)	Yes	Yes
SMS MFA	Yes	Yes	Phone auth	Yes	Plugin	Yes
Push MFA	Guardian app	No	No	No	No	No
Biometric	Via WebAuthn	Via WebAuthn	No	No	Via WebAuthn	Via WebAuthn

Enterprise Features

Feature	Auth0	Clerk	Supabase Auth	Firebase Auth	Keycloak	FusionAuth
SAML SSO	Yes	Yes (paid)	No	No	Yes	Yes
OIDC SSO	Yes	Yes	No	No	Yes	Yes
SCIM provisioning	Yes (Enterprise)	Yes (paid)	No	No	Yes	Yes (paid)
Organizations/tenants	Yes	Yes	No (manual)	No	Realms	Yes
Custom domains	Yes	Yes	Yes	No	Yes	Yes
Branding/theming	Universal Login	Pre-built components	Basic	Basic	Themes	Themes
Breached password detection	Yes	Yes	No	No	Plugin	Yes
Bot detection	Yes (captcha)	Smart bot protection	No	No	No	Yes (paid)

Developer Experience

Feature	Auth0	Clerk	Supabase Auth	Firebase Auth	Keycloak	FusionAuth
Setup time	30 min	15 min	15 min	15 min	1-2 hours	30 min
React SDK	Yes	Excellent	Yes	Yes	Community	Yes
Next.js support	Good	Excellent	Good	Good	Community	Good
React Native	Yes	Yes	Yes	Excellent	Community	Yes
API quality	Excellent	Excellent	Good	Good	Good	Excellent
Documentation	Excellent	Excellent	Good	Good	Good	Excellent
TypeScript support	Good	Excellent	Good	Good	N/A	Good
Pre-built UI components	Universal Login	Full component library	Basic	FirebaseUI	Themes	Community
Webhooks	Yes	Yes	Postgres triggers	Cloud Functions	Events	Yes

Self-Hosted vs Managed

Provider	Self-Hosted	Managed Cloud	Air-Gapped
Auth0	No (Private Cloud is managed)	Yes	No
Clerk	No	Yes	No
Supabase Auth	Yes (open source)	Yes	Yes
Firebase Auth	No	Yes (GCP only)	No
Keycloak	Yes (primary model)	Third-party managed	Yes
FusionAuth	Yes (Community edition)	Yes	Yes

Provider Deep Dives

Auth0

Best for: Mid-to-large companies needing enterprise SSO and compliance.

Strengths:
- Most comprehensive enterprise feature set
- 50+ social login providers
- Actions (serverless hooks for custom logic)
- Universal Login (customizable hosted login page)
- SOC 2 Type II, HIPAA BAA, ISO 27001 certified

Weaknesses:
- Expensive at scale ($23/1000 MAU on Professional plan)
- Complex pricing model (features gated by tier)
- Lock-in risk (Actions API is proprietary)
- Migration out is painful (custom connection logic)

Clerk

Best for: Modern web apps (Next.js, React) prioritizing developer experience and pre-built UI.

Strengths:
- Best-in-class React/Next.js components
- 15-minute setup with full auth UI
- Organizations and multi-tenancy built in
- Excellent TypeScript SDK
- Session management with device tracking

Weaknesses:
- Newer company (founded 2020)
- Limited enterprise features compared to Auth0
- No self-hosted option
- Smaller community and ecosystem
- Pricing can be high for large consumer apps

Supabase Auth

Best for: PostgreSQL-native applications and teams already using Supabase.

Strengths:
- Free tier (50,000 MAU)
- Open source (GoTrue)
- Deep PostgreSQL integration (Row Level Security)
- Self-hostable
- Simple API

Weaknesses:
- No SAML/SCIM (enterprise SSO gap)
- Limited MFA (TOTP only, added late)
- No organizations/multi-tenancy
- Basic UI components
- GoTrue is a simpler auth server than Auth0/Keycloak

Firebase Auth

Best for: Mobile-first applications in the Google ecosystem.

Strengths:
- Excellent mobile SDKs (iOS, Android, Flutter)
- Free tier (no cost for most auth features)
- Anonymous authentication for gradual onboarding
- Phone authentication with global SMS
- Deep GCP integration

Weaknesses:
- No SAML, SCIM, or enterprise SSO
- No WebAuthn/passkeys
- Limited customization
- GCP vendor lock-in
- No self-hosted option
- Firebase ecosystem is required

Keycloak

Best for: Organizations requiring full control, self-hosting, and enterprise features without per-user pricing.

Strengths:
- Completely free and open source (Apache 2.0)
- Full SAML + OIDC + SCIM support
- Multi-realm (multi-tenant) architecture
- Identity brokering (federate with any IdP)
- LDAP/Active Directory integration
- No per-user pricing

Weaknesses:
- Significant operational burden (Java, requires DB, clustering)
- Steep learning curve
- UI is functional but not modern
- No managed cloud offering from Red Hat (community managed options exist)
- Customization requires Java SPI knowledge
- Resource-heavy (JVM memory requirements)

FusionAuth

Best for: Companies that want enterprise features at a lower cost than Auth0, with self-hosting option.

Strengths:
- Self-hosted Community Edition is free
- Enterprise features at lower price than Auth0
- Excellent API documentation
- Advanced threat detection (paid)
- Multi-tenant architecture
- Fast setup

Weaknesses:
- Smaller ecosystem than Auth0/Keycloak
- Community edition lacks some features (SCIM, advanced MFA)
- Less third-party integration content
- Smaller community

Pricing Comparison (as of 2026)

Provider	Free Tier	Starter/Pro	Enterprise	Model
Auth0	25,000 MAU	$240/mo (Essential)	Custom	Per MAU
Clerk	10,000 MAU	$25/mo + $0.02/MAU	Custom	Per MAU
Supabase Auth	50,000 MAU	$25/mo (Pro)	Custom	Per project
Firebase Auth	Unlimited (basic)	Pay per verification (phone)	N/A	Per verification
Keycloak	Unlimited (self-host)	N/A	N/A	Free (infra costs)
FusionAuth	Unlimited (self-host)	$125/mo (Starter)	Custom	Per deployment

Cost at Scale

At 100,000 MAU, approximate monthly costs:

Auth0 Professional: ~$2,300/mo
Clerk Pro: ~$1,825/mo
Supabase Pro: ~$25/mo (auth is included in project pricing)
Firebase: ~$0 (basic auth is free)
Keycloak: ~$200-500/mo (infrastructure only)
FusionAuth Community: ~$200-500/mo (infrastructure only)

Vendor Lock-In Risks

What Creates Lock-In

Lock-In Vector	Risk Level	Mitigation
User data format	Medium	Export users regularly; ensure email/password are standard
Password hashes	High	Providers may use proprietary hash formats; migration requires password reset
Custom hooks/actions	High	Business logic in provider-specific serverless functions
Social login tokens	Low	Re-link social accounts on migration
SSO configurations	Medium	SAML/OIDC metadata must be reconfigured per customer
SDK integration depth	Medium	Deep SDK usage = more code to change
Session format	Low	Sessions can be migrated or expired

Abstraction Layer

Build a thin abstraction over your auth provider to reduce lock-in:

typescript

// auth-adapter.ts — Provider-agnostic interface
interface AuthProvider {
  // User management
  createUser(data: CreateUserData): Promise<User>;
  getUserById(id: string): Promise<User | null>;
  getUserByEmail(email: string): Promise<User | null>;
  updateUser(id: string, data: Partial<User>): Promise<User>;
  deleteUser(id: string): Promise<void>;

  // Authentication
  verifyToken(token: string): Promise<TokenPayload>;
  refreshToken(refreshToken: string): Promise<TokenPair>;

  // MFA
  enrollMFA(userId: string, method: MFAMethod): Promise<MFAEnrollment>;
  verifyMFA(userId: string, code: string): Promise<boolean>;

  // SSO
  getSSOConfig(tenantId: string): Promise<SSOConfig>;
  handleSSOCallback(data: SSOCallbackData): Promise<User>;
}

// Implementations
class Auth0Adapter implements AuthProvider { /* ... */ }
class ClerkAdapter implements AuthProvider { /* ... */ }
class KeycloakAdapter implements AuthProvider { /* ... */ }

Abstraction Limits

The abstraction layer helps with basic operations but cannot fully isolate provider-specific features (Auth0 Actions, Clerk Organizations, Keycloak Realms). Accept that some lock-in is unavoidable and factor migration cost into provider selection.

Migration Strategies

Migration Types

Gradual Migration (Recommended)

typescript

async function handleLogin(email: string, password: string): Promise<User> {
  // Check if user has been migrated
  const migrated = await db.users.findByEmail(email);

  if (migrated?.authProvider === 'new_provider') {
    // User already migrated — use new provider
    return newProvider.authenticate(email, password);
  }

  // User still on old provider
  const user = await oldProvider.authenticate(email, password);

  if (user) {
    // Successful login — migrate now (lazy migration)
    await newProvider.createUser({
      email: user.email,
      // Set password in new provider (we have it in plaintext during login)
      password,
      metadata: user.metadata,
    });

    await db.users.update(user.id, { authProvider: 'new_provider' });

    return user;
  }

  throw new AuthError('Invalid credentials');
}

Password Hash Migration

The hardest part of any auth migration is passwords. You cannot export password hashes from most managed providers. Options:

Strategy	User Impact	Complexity	Timeline
Lazy migration (re-hash on next login)	None — transparent to user	Medium	Months (some users never log in)
Forced password reset	High — all users must reset	Low	Days
Hash import (if formats are compatible)	None	High	Days
Parallel auth (try both providers)	None	Medium	Months

Selection Checklist

Use this checklist to score providers for your specific needs:

Criterion	Weight (1-5)	Your Score
Free tier sufficient for MVP?	3
Supports your framework (Next.js, etc.)?	5
Enterprise SSO (SAML/OIDC)?	4 (B2B) / 1 (B2C)
SCIM provisioning?	3 (B2B) / 0 (B2C)
Self-hosting available?	2-5 (varies)
MFA methods you need?	4
Pricing at your 12-month MAU projection?	5
Compliance certifications needed?	4
Pre-built UI quality?	3
Migration path out?	3
Community and support quality?	3
Passkey support?	3

Auth Provider Comparison ​

Build vs Buy Decision Framework ​

When to Buy (Use a Provider) ​

When to Build ​

The Hybrid Approach ​

Feature Comparison Matrix ​

Core Authentication Features ​

Enterprise Features ​

Developer Experience ​

Self-Hosted vs Managed ​

Provider Deep Dives ​

Auth0 ​

Clerk ​

Supabase Auth ​

Firebase Auth ​

Keycloak ​

FusionAuth ​

Pricing Comparison (as of 2026) ​

Vendor Lock-In Risks ​

What Creates Lock-In ​

Abstraction Layer ​

Migration Strategies ​

Migration Types ​

Gradual Migration (Recommended) ​

Password Hash Migration ​

Selection Checklist ​

Further Reading ​