Supabase Auth: AI-Optimized Technical Reference

Core Technology Overview

What it is: PostgreSQL-based authentication service that stores users in queryable database tables instead of vendor-locked systems.

Key differentiator: Row Level Security (RLS) enforces permissions at database level - bypassing APIs, middleware, or frontend still applies security policies.

Critical Advantages vs Competitors

Database Integration Reality

• Users stored in standard PostgreSQL auth.users table
• Direct SQL queries: SELECT COUNT(*) FROM auth.users WHERE created_at > now() - interval '7 days'
• GDPR compliance: COPY auth.users TO '/tmp/users.csv' CSV HEADER
• Failure prevention: No vendor-specific export APIs or enterprise tier requirements for data access

JWT Token Implementation

• Standard JWT format with RSA signing (no shared secrets to leak)
• Clean token structure without vendor metadata bloat
• 1-hour expiration with automatic refresh
• Breaking point: Safari blocks third-party cookies, breaks embedded auth flows

Pricing Reality Check (2025)

Provider	Free Tier MAU	Pro Tier Cost	25K Users Cost	100K Users Cost
Supabase	50,000	$25/mo	$0	$25/mo
Auth0	7,500	$70/mo	$175/mo	$700+/mo
AWS Cognito	50,000	Pay per use	$137/mo	$550/mo
Firebase	50,000	$0.0055/MAU	$137.50/mo	$550/mo
Clerk	10,000	$25/mo	$65/mo	$325/mo

Hidden costs:

• SMS MFA: $0.05 per message (TOTP apps are free alternative)
• Enterprise features included in Pro tier (unlike competitors)

Row Level Security (RLS) Implementation

Critical Success Pattern

-- Enable RLS (required first step)
ALTER TABLE profiles ENABLE ROW LEVEL SECURITY;

-- User isolation (bulletproof pattern)
CREATE POLICY "users_own_data" ON profiles
  FOR ALL USING (auth.uid() = user_id);

-- Team access (80% use case)
CREATE POLICY "team_access" ON posts
  FOR ALL USING (
    EXISTS (
      SELECT 1 FROM team_members 
      WHERE user_id = auth.uid() 
      AND team_id = posts.team_id
    )
  );

Fatal Gotcha

Problem: RLS policies are allowlists - no matching policy = empty results with no error
Debugging: Use SELECT set_config('request.jwt.claims', '{"sub":"real-user-uuid","role":"authenticated"}', true) to test policies

Setup Configuration That Won't Break

Client Configuration

// lib/supabase.ts - Production-ready config
import { createClient } from '@supabase/supabase-js'

export const supabase = createClient(supabaseUrl, supabaseKey, {
  auth: {
    persistSession: true,
    autoRefreshToken: true,
    detectSessionInUrl: true
  }
})

OAuth Provider Setup

Redirect URL pattern: https://[project-ref].supabase.co/auth/v1/callback

Common failures:

• Case sensitivity in redirect URLs (localhost vs Localhost)
• GitHub OAuth requires org approval for work accounts
• Google OAuth needs domain verification for production
• Enabled provider in dashboard but forgot to configure credentials

Production Failure Modes

Email System Failures

Default behavior: Supabase email works in dev, silently fails in production
Required: Custom SMTP configuration from day one
Failure scenarios:

• Gmail SMTP: 100 emails/day limit → signups stop working silently
• Rate limiting during bulk operations → 100 invites sent, 3 delivered
• Confirmation emails in spam → users blame app

Authentication Edge Cases

1. JWT refresh loops: Token refresh fails → infinite redirect loops
2. Silent email failures: SMTP blocking → no signup capability, no logs
3. Safari cookie blocking: Third-party cookies disabled → embedded auth broken
4. CORS domain mismatch: Works on app.domain.com, fails on domain.com
5. Rate limit lockouts: 5 failed attempts → 24-hour user lockout

Resource Scaling Limits

What works: Login/registration for thousands of concurrent users
What breaks first:

• Real-time connections (shared infrastructure limits)
• Database connections (requires connection pooling)
• Email delivery (SMTP provider bottlenecks)

Feature Completeness Matrix

Feature	Supabase	Notes
Multi-Factor Auth	✅ TOTP, SMS	SMS costs extra, TOTP free
Enterprise SSO	✅ SAML 2.0	Included in Pro tier
Phone Auth	✅ SMS providers	Twilio, MessageBird, Vonage
Magic Links	✅ Email-based	Passwordless authentication
Anonymous Auth	✅ Guest conversion	Convert anonymous to full accounts
Web3 Auth	✅ Solana wallets	Crypto wallet integration
Custom SMTP	✅ Required for prod	Default email fails in production

Decision Criteria

Choose Supabase Auth When:

• Using PostgreSQL (or can migrate)
• Need database-integrated authentication
• Cost-sensitive (enterprise features without enterprise prices)
• Want SQL-queryable user data
• Row Level Security appeals for security architecture

Look Elsewhere When:

• Deep in different ecosystem (AWS DynamoDB, Firebase)
• Need identity federation across hundreds of enterprise systems
• Cannot use PostgreSQL
• Migration costs outweigh benefits

Implementation Time Investment

Basic setup: 15 minutes
Production debugging: 15+ hours
Migration from Firebase: 2-4 weeks (document structure conversion pain)
Enterprise features: Included in Pro tier (not additional development time)

Critical Production Requirements

Monitoring Essentials

-- Failed login detection (potential attacks)
SELECT COUNT(*), user_agent, ip_address
FROM auth.audit_log_entries
WHERE action = 'login' AND result = 'failure'
AND created_at > now() - interval '1 hour'
GROUP BY user_agent, ip_address
HAVING COUNT(*) > 10;

Error Handling Patterns

const handleAuthError = (error: AuthError) => {
  switch (error.message) {
    case 'Invalid login credentials':
      return 'Email or password is incorrect'
    case 'Email not confirmed':
      return 'Please check your email and click the confirmation link'
    case 'Signup not allowed for this instance':
      return 'Registration is currently disabled'
    default:
      console.error('Auth error:', error)
      return 'An error occurred. Please try again.'
  }
}

Security Assessment

Production-ready security: Yes, with proper RLS policy implementation
Standard compliance: JWT tokens, bcrypt passwords, PostgreSQL RLS
Enterprise validation: Used by 1Password, Mozilla
Vulnerability: Poor RLS policies create security holes
Advantage: Database-level security cannot be bypassed by API bugs

Migration Considerations

From Firebase: Complex (NoSQL to SQL structure conversion required)
From Auth0: Medium complexity (similar JWT structure)
From custom auth: Low complexity (standard PostgreSQL integration)
Exit strategy: Open source + standard PostgreSQL = easy data export

Resource Requirements

Development expertise: PostgreSQL knowledge essential for RLS policies
Infrastructure: Managed PostgreSQL included
Maintenance: Self-hosting complex, defeats purpose
Support: Active Discord community (50K+ developers), GitHub issues

Critical Success Factors

1. Configure custom SMTP immediately - default email fails in production
2. Test RLS policies with real user context - allowlist nature hides errors
3. Plan for OAuth provider quirks - each has specific configuration gotchas
4. Monitor authentication metrics - silent failures are common
5. Budget debugging time - production edge cases require extensive testing