Auth Libraries: Open Source vs Paid

// Best for: Next.js projects
// Pros: Free, many providers, active community
// Cons: Next.js focused, config can be complex

import NextAuth from "next-auth";
import GitHub from "next-auth/providers/github";

export const { handlers, auth } = NextAuth({
  providers: [GitHub],
});

// Best for: Full control, any framework
// Pros: Lightweight, framework agnostic, type-safe
// Cons: More manual setup, newer

import { Lucia } from "lucia";

const lucia = new Lucia(adapter, {
  sessionCookie: {
    attributes: { secure: true }
  }
});

const session = await lucia.createSession(userId, {});

// Best for: Enterprise, SSO, multiple apps
// Pros: Full IAM solution, SAML/OIDC, free
// Cons: Heavy, complex setup, Java-based

// Usually configured via admin console
// Then connect via OIDC
const keycloak = new Keycloak({
  realm: "my-realm",
  url: "https://keycloak.example.com",
  clientId: "my-app"
});

// Best for: Quick setup, good docs
// Pros: Easy, many features, great docs
// Cons: Gets expensive fast, vendor lock-in

import { Auth0Client } from "@auth0/auth0-spa-js";

const auth0 = new Auth0Client({
  domain: "your-tenant.auth0.com",
  clientId: "YOUR_CLIENT_ID"
});

await auth0.loginWithRedirect();

// Best for: Beautiful pre-built UI
// Pros: Gorgeous components, fast setup
// Cons: Expensive, less customizable

import { SignIn } from "@clerk/nextjs";

// That's it - pre-built UI
<SignIn />

// Or hooks
const { user } = useUser();

// Best for: Full-stack with database
// Pros: Generous free tier, PostgreSQL included
// Cons: Tied to Supabase ecosystem

import { createClient } from "@supabase/supabase-js";

const supabase = createClient(URL, KEY);

await supabase.auth.signInWithOAuth({
  provider: "google"
});