Authentication API Comparison 2026

How Authentication APIs Work

The typical OAuth/OIDC authentication flow

Common Use Cases

Why developers need authentication APIs

Feature Comparison

Side-by-side comparison of authentication services

Provider Deep Dives

Detailed breakdown of each authentication service

Self-Hosted vs Managed Auth

When to self-host vs when to use a managed service

Code Examples

Get started with each authentication provider

Email/Password Signup

// Install: npm install @auth0/nextjs-auth0
// pages/api/auth/[...auth0].js
import { handleAuth } from '@auth0/nextjs-auth0';

export default handleAuth();

// pages/_app.js
import { UserProvider } from '@auth0/nextjs-auth0/client';

export default function App({ Component, pageProps }) {
  return (
    <UserProvider>
      <Component {...pageProps} />
    </UserProvider>
  );
}

// Any page - check auth
import { useUser } from '@auth0/nextjs-auth0/client';

export default function Profile() {
  const { user, isLoading } = useUser();
  if (isLoading) return <div>Loading...</div>;
  if (!user) return <a href="/api/auth/login">Login</a>;
  return <div>Welcome {user.name}!</div>;
}

// Install: npm install @clerk/nextjs
// middleware.ts
import { clerkMiddleware } from '@clerk/nextjs/server';
export default clerkMiddleware();

// app/layout.tsx
import { ClerkProvider, SignInButton, UserButton }
  from '@clerk/nextjs';

export default function Layout({ children }) {
  return (
    <ClerkProvider>
      <header>
        <SignInButton />
        <UserButton />
      </header>
      {children}
    </ClerkProvider>
  );
}

// Protect a page
import { auth } from '@clerk/nextjs/server';

export default async function Dashboard() {
  const { userId } = await auth();
  if (!userId) redirect('/sign-in');
  return <div>Protected content</div>;
}

// Install: npm install firebase
import { initializeApp } from 'firebase/app';
import {
  getAuth, createUserWithEmailAndPassword,
  signInWithEmailAndPassword, signInWithPopup,
  GoogleAuthProvider
} from 'firebase/auth';

const app = initializeApp({
  apiKey: "your-api-key",
  authDomain: "your-project.firebaseapp.com",
  projectId: "your-project"
});
const auth = getAuth(app);

// Sign up with email
const { user } = await createUserWithEmailAndPassword(
  auth, "user@example.com", "password123"
);

// Sign in with Google
const result = await signInWithPopup(
  auth, new GoogleAuthProvider()
);
console.log(result.user.displayName);

// Install: npm install @supabase/supabase-js
import { createClient } from '@supabase/supabase-js';

const supabase = createClient(
  'https://your-project.supabase.co',
  'your-anon-key'
);

// Sign up with email
const { data, error } = await supabase.auth.signUp({
  email: 'user@example.com',
  password: 'password123'
});

// Sign in with Google
const { data } = await supabase.auth.signInWithOAuth({
  provider: 'google'
});

// Get current user
const { data: { user } } = await supabase.auth.getUser();

// Protected query with RLS
const { data: posts } = await supabase
  .from('posts')
  .select('*');
// Only returns rows the user has access to!

Social Login (Google)

// Auth0 handles social login through Universal Login
// Just configure Google in your Auth0 dashboard
// Then redirect to login:

// Frontend - redirect to Auth0
window.location.href = `https://YOUR_DOMAIN.auth0.com/authorize?
  response_type=code&
  client_id=YOUR_CLIENT_ID&
  redirect_uri=http://localhost:3000/callback&
  scope=openid profile email&
  connection=google-oauth2`;

// Backend - exchange code for tokens
const response = await fetch('https://YOUR_DOMAIN.auth0.com/oauth/token', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    grant_type: 'authorization_code',
    client_id: 'YOUR_CLIENT_ID',
    client_secret: 'YOUR_CLIENT_SECRET',
    code: authorizationCode,
    redirect_uri: 'http://localhost:3000/callback'
  })
});

# Start Keycloak with Docker
docker run -p 8080:8080 \
  -e KC_BOOTSTRAP_ADMIN_USERNAME=admin \
  -e KC_BOOTSTRAP_ADMIN_PASSWORD=admin \
  quay.io/keycloak/keycloak:latest start-dev

# Configure Google IdP in admin console:
# 1. Go to http://localhost:8080/admin
# 2. Identity Providers > Google
# 3. Add Client ID and Secret from Google Console

# Use Keycloak JS adapter in frontend:
import Keycloak from 'keycloak-js';

const keycloak = new Keycloak({
  url: 'http://localhost:8080',
  realm: 'my-realm',
  clientId: 'my-app'
});

await keycloak.init({ onLoad: 'login-required' });
console.log('Authenticated:', keycloak.authenticated);
console.log('User:', keycloak.tokenParsed.preferred_username);

# Step 1: Redirect user to Google's OAuth consent screen
# (This happens in the browser, not cURL)
# https://accounts.google.com/o/oauth2/v2/auth?
#   client_id=YOUR_CLIENT_ID&
#   redirect_uri=http://localhost:3000/callback&
#   response_type=code&
#   scope=openid+email+profile

# Step 2: Exchange authorization code for tokens
curl -X POST https://oauth2.googleapis.com/token \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -d "code=AUTHORIZATION_CODE" \
  -d "client_id=YOUR_CLIENT_ID" \
  -d "client_secret=YOUR_CLIENT_SECRET" \
  -d "redirect_uri=http://localhost:3000/callback" \
  -d "grant_type=authorization_code"

# Step 3: Get user info with access token
curl https://www.googleapis.com/oauth2/v2/userinfo \
  -H "Authorization: Bearer ACCESS_TOKEN"

# Response: {"id":"...","email":"user@gmail.com","name":"..."}

Pricing at Scale

What you'll pay as your user base grows

Prices approximate. SSO pricing is for enterprise SAML/OIDC connections. Server costs for Keycloak assume cloud VPS. Check provider websites for current pricing.

Which Auth Service Should You Use?

Quick decision guide based on your situation

Frequently Asked Questions