Authentication is one of the first features every startup needs. In 2025, web products are built with TypeScript-first stacks like Next.js, React Router, and TanStack Start, so teams expect strong type safety, flexible hosting, and ownership of user data.

This article reviews the top free, open-source authentication libraries used by modern web apps — with practical advice on when each one shines.

We’ll focus on:

• Better Auth (TypeScript-first, feature-rich)
• Auth.js (NextAuth) (easy social auth for Next.js)
• Supabase Auth (managed backend + auth)
• SuperTokens (customizable, self-hosted)

Quick Comparison#

Better Auth — TypeScript-First & Full-Featured#

Better Auth is the most flexible, modern option if you’re building a full-stack TypeScript app and want long-term scalability.

Why devs choose it:

• Multiple auth strategies supported from day one
• Database-agnostic (Postgres, MySQL, SQLite, Drizzle, Prisma, etc.)
• Plugin ecosystem for 2FA, phone OTP, organization roles, audit logs, etc.
• Same code works with Next.js, TanStack Start, Express, etc.

Setup Example — Next.js#

// lib/auth.ts
import { betterAuth } from "better-auth";
import { Pool } from "pg";

export const auth = betterAuth({
  database: new Pool({
    connectionString: process.env.DATABASE_URL,
  }),
  emailAndPassword: { enabled: true },
  socialProviders: ["github", "google"],
  appName: "MyProduct",
});

// app/api/auth/[...all]/route.ts
import { auth } from "@/lib/auth";
import { toNextJsHandler } from "better-auth/next-js";

export const { GET, POST } = toNextJsHandler(auth.handler);

Client usage:

import { createAuthClient } from "better-auth/react";
export const authClient = createAuthClient();

const session = authClient.useSession();

When Better Auth is the best choice#

• You need 2FA / passkeys / advanced policies
• You want to own the user database entirely
• You might expand to B2B teams, roles, multi-tenant features
• You want React + TS type safety across the stack

Auth.js (NextAuth) — Easiest Social Login for Next.js#

Auth.js is the OG leader for Next.js authentication, made famous for how quickly you can add providers.

Minimal GitHub login example#

// pages/api/auth/[...nextauth].ts
import NextAuth from "next-auth";
import GitHub from "next-auth/providers/github";

export default NextAuth({
  providers: [GitHub({ clientId, clientSecret })],
});

Why devs like it

• Dead-simple setup
• Wide provider support
• Built-in UI pages

Trade-offs

• Does not provide MFA or org management by default
• Heavy callback configurations for anything custom
• Deeply tied to Next.js (less portable)

Best for:#

Early-stage teams shipping a marketing site or SaaS MVP built on Next.js.

Supabase Auth — Auth Inside a Backend Platform#

Supabase Auth is part of Supabase’s Postgres-based platform (DB, storage, realtime).

import { createClient } from "@supabase/supabase-js";
const supabase = createClient(url, anonKey);

await supabase.auth.signInWithPassword({ email, password });

Strengths

• Everything is hosted and integrated
• Easy social login setup in the Supabase dashboard
• RLS permissions enforced directly in the DB

Limitations

• More platform-lock-in than library-level solutions
• UI customization requires wiring up client SDK events manually

Best for:#

Startups that want auth + backend + admin UI without engineering DevOps.

SuperTokens — The Self-Hosted Customizer#

SuperTokens is OSS and built for projects that need full control over auth flows.

import SuperTokens from "supertokens-node";
import Session from "supertokens-node/recipe/session";
import ThirdPartyEmailPassword from "supertokens-node/recipe/thirdpartyemailpassword";

SuperTokens.init({
  supertokens: { connectionURI: process.env.SUPERTOKENS_URI },
  recipeList: [Session.init(), ThirdPartyEmailPassword.init()],
});

Pros

• Granular overrides
• Enterprise-style session management
• Flexible frontend SDK

Cons

• More setup, more plumbing
• Adds noticeable JS bundle weight

Best for:#

Applications with atypical auth flows that require full customization.

Which One Should Your Startup Choose?#

Final Recommendation#

If your startup is building a Next.js or TypeScript-first product, and you expect to grow into features like multi-tenant roles, MFA, phone verification, passkeys, or custom session policies, then:

Better Auth is the strongest long-term open-source solution in 2025.

But — if you just need Google login by tonight? Start with Auth.js or Supabase Auth, then move up when needed.