Top 10 Authentication Services and Libraries in 2026: From Free to Enterprise

Table of Contents

• Why choosing auth in 2026 feels like picking a car seat
• How to read this list
• Passport.js
• Lucia
• Okta Customer Identity Cloud
• AWS Cognito
• Keycloak
• NextAuth.js / Auth.js
• Auth0
• Firebase Auth
• Clerk
• Supabase Auth
• Frequently Asked Questions

How to read this list

Think of this section as the installation manual, not the marketing sticker on the box. The “Top 10” that follows isn’t a universal ranking; it’s organized around where each option actually fits: side projects, SaaS startups, or enterprise stacks. Your job is to skim this once, decide which “vehicle” you’re driving (Next.js on Vercel, React Native with Firebase, AWS-heavy backend, on-prem enterprise), and then read the individual entries through that lens.

The three big “fit” questions

Before you compare features, it helps to frame every auth choice around three tradeoffs you can’t avoid. First is control vs convenience: SaaS platforms like Auth0, Clerk, Firebase, Supabase, Cognito, and Okta CIC are like click-in seats - fast to install, opinionated, and maintained for you. Open-source and self-hosted options (NextAuth/Auth.js, Passport, Lucia, Keycloak) are more like threading the belt by hand: more work, but you see every strap and buckle. Second is free now vs predictable cost at 100K MAUs; many tools look inexpensive at 1K users but become painful as you grow. Third is modern UX vs legacy compatibility: passwordless flows, WebAuthn, and adaptive MFA are rapidly becoming the default, while older, clunkier flows quietly drive user drop-off. An authentication trends piece from Authsignal warns that, in this era, companies with clunky UX “will get left behind,” as users now expect seamless, low-friction sign-ins (Authsignal’s 2026 authentication trends).

“In 2026, UX becomes the primary differentiator. Companies building solutions with clunky UX will get left behind.” - Founder perspective, Authsignal

Reading the MAU pricing table without getting surprised

The quick-glance pricing below focuses on approximate monthly costs at around 1K, 10K, and 100K Monthly Active Users (MAUs). These numbers come from each provider’s published pricing and independent breakdowns, and they intentionally ignore SMS fees and edge cases so you can compare the general shape of costs. Treat them like the “weight and height limits” printed in tiny text on the side of a car seat: they don’t matter much on day one, but they matter a lot once your app starts growing or you add phone-based MFA. Security Boulevard’s deep dive into Auth0’s plans even notes that many startups experience its pricing as a kind of “growth penalty” once they move past the free tier, because costs ramp steeply as MAUs and feature use increase (Auth0 pricing analysis on Security Boulevard).

Open-source and self-hosted options (NextAuth/Auth.js, Passport.js, Lucia, Keycloak) are “free” in licensing but cost you in time, hosting, monitoring, and security patching. In practice, most beginners and career-switchers should learn with at least one SaaS provider and one open-source option, using AI copilots to help with snippets and boilerplate while you focus on understanding HTTP, sessions vs tokens, and OAuth/OIDC flows. Those fundamentals are what let you read tables like this critically, spot where the real limits and overages hide, and choose the auth “seat” that fits your stack and your budget instead of whatever your AI happened to autocomplete first.

Passport.js

Passport.js is the belt-routed, old-school convertible seat of the Node ecosystem: it fits almost any Node/Express “vehicle,” but you’re threading every strap yourself. For beginners and career-switchers, that can be intimidating - and also exactly what forces you to understand what’s really happening with cookies, sessions, and OAuth instead of hiding behind a glossy dashboard.

Best if…

You’re working on a classic Node/Express app (or Nest/Koa) where you want maximum flexibility, need to plug into things like LDAP or custom OAuth providers, and you’re willing to own the session management and database layer yourself instead of paying per MAU to a SaaS platform.

Quick facts

• Category: Open-source library (MIT license)
• Pricing: Free; you host and maintain everything
• Ecosystem: Over 500+ “strategies” for social logins, LDAP, SAML, and local auth, highlighted in this overview of open-source auth tools
• Frameworks: Node.js (Express, Koa, NestJS, and more)
• Integration difficulty: Moderate - you wire sessions, persistence, and error handling by hand

Standout strengths

• Huge strategy catalog: If it speaks OAuth, SAML, LDAP, or some obscure enterprise protocol, there’s probably a Passport strategy for it, which is why open-source roundups still list it among the most flexible auth options for Node.
• Fine-grained control: You decide how to store users and sessions - MongoDB, Postgres, Redis, or something else - and you control token lifetimes, cookie flags, and login flows in code.
• Foundational learning value: For Nucamp-style learners, building auth with Passport is a crash course in HTTP, redirects, callbacks, and sessions vs JWTs. AI copilots can generate middleware, but you’ll still need to reason about where to store session IDs and how to protect them.

Watch out for…

• Boilerplate and fragmentation: Compared to newer, batteries-included libraries like Auth.js or BaaS platforms like Supabase, you’ll write a lot of glue code - serializing users, handling errors, building login/logout/register pages from scratch.
• No built-in UI or console: There’s no hosted dashboard, metrics view, or drop-in components; everything from password reset flows to “remember me” checkboxes is your responsibility. A broader survey of open-source auth tools from Cerbos’ 2026 enterprise auth guide emphasizes that this tradeoff - flexibility in exchange for more operational work - is common across self-managed stacks.
• Modern flows need extra work: Passwordless UX, WebAuthn, or strong phishing-resistant MFA aren’t first-class here; you’ll be composing multiple libraries and patterns yourself.

Practical example: Legacy monolith with LDAP + Google login

Imagine you join a team maintaining a legacy on-prem Node.js app inside a mid-sized company. Employees must authenticate with corporate LDAP, while contractors sign in with Google Workspace. Passport lets you mount an LDAP strategy for staff and a Google OAuth 2.0 strategy for contractors, then back both with a shared session store in Redis so multiple app servers can recognize the same user.

AI tools can scaffold the Express routes and Passport middleware, but they won’t decide what to do when LDAP is down, how long sessions should last, or how to prevent session fixation. Understanding those details - and being able to explain them in an interview - turns “used Passport.js” on your portfolio from a line item into evidence that you really grasp the straps and buckles of web authentication, not just the shiny plastic shell.

Lucia

Lucia is the minimalist, no-extra-padding car seat that assumes you actually read the manual. It hands you the straps and anchor points for auth and sessions, but expects you to decide exactly how everything bolts into your app. For beginners who are ready to get past “click next in a SaaS dashboard,” Lucia is a gentle way to learn the fundamentals without the bloat of a full identity platform.

Best if…

You want maximum control over your auth schema and sessions, you’re comfortable managing a database, and you’re building with modern frameworks like SvelteKit, Next.js, or Astro. It’s especially attractive if you’re wary of SaaS lock-in and like the idea of your identity data living entirely in your own Postgres/MySQL/SQLite instance, not someone else’s multi-tenant cluster.

Quick facts

• Category: Open-source library
• Pricing: Free; you pay only for hosting and your database
• Features: Unopinionated session management, full control over tables and columns, framework-agnostic
• Frameworks: SvelteKit, Next.js, Astro, and other modern web stacks
• Integration difficulty: Moderate - more setup than SaaS, but less ceremony than older tools like Passport

Standout strengths

• Zero vendor lock-in: Your user and session data live in a database you own, with a schema you design. If you ever migrate to a different stack, you’re not untangling tenant IDs and opaque metadata from a SaaS provider.
• Clean mental model: Lucia gives you primitives instead of a giant control panel: session issuance, validation, and revocation are explicit in code, which is great for understanding how auth actually works rather than clicking around a UI.
• Modern framework fit: It lines up well with the server-centric patterns in tools like SvelteKit and the app router in Next.js, which are front and center in many modern full-stack tutorials and in comparisons like Zsolt Ero’s breakdown of auth providers.

Watch out for…

• No drop-in UI or console: There’s no hosted dashboard, analytics, or prebuilt sign-in widgets. You’ll build the entire UX yourself - which AI can help scaffold - but you still need to think through password resets, onboarding, and error states.
• You own security posture: Cookie flags, session lifetimes, CSRF protection, and password policies are your responsibility. As enterprise-focused comparisons on sites like Feathery’s Auth0 alternatives guide point out, this is the classic tradeoff: ultimate flexibility in exchange for doing your own hardening and monitoring.
• Fewer batteries included than SaaS: Features like organization management, fine-grained MFA options, or analytics require additional libraries and services; Lucia stays intentionally small.

Practical example: Privacy-focused indie SaaS

Imagine you’re building a small, privacy-first SaaS aimed at European customers who care deeply about where their data lives. You deploy SvelteKit to a region-specific host, run Postgres in the same region, and wire Lucia directly to a minimal user table: email, hashed password, consent flags. Sessions are stored server-side only, with strict cookies, so nothing sensitive leaks into localStorage. An AI copilot can help you write the SvelteKit endpoints and Lucia calls, but you’re the one deciding how long sessions last, when to invalidate them, and how to add WebAuthn or magic links later without handing your user database to a third party.

From a hiring perspective, listing Lucia on your portfolio signals that you’ve gone beyond clicking through a wizard. It shows you’ve made real decisions about schemas, sessions, and security tradeoffs - skills that transfer directly to more widely used stacks like Auth.js, Supabase Auth, or Firebase once you’re on a larger team.

Okta Customer Identity Cloud

Okta Customer Identity Cloud (which includes Auth0) is the fully loaded travel system of auth: stroller, infant seat, and base all bundled together. It’s overkill for a quick grocery run, but if you’re dealing with big-company realities - multiple apps, partner SSO, compliance audits - it’s exactly the kind of high-end, tightly engineered gear those environments expect.

Best if…

• You’re at a mid-to-large enterprise that already uses Okta or similar tools for workforce SSO and wants a unified platform for both employees and customers.
• Your product needs B2B SSO, directory integration, and strong compliance (SOC 2, HIPAA, PCI-DSS) rather than just simple email/password logins.

Quick facts

Okta Customer Identity Cloud is an enterprise SaaS IAM platform with a free developer tier that typically covers about 1,000-7,500 MAUs for experimentation and small pilots. Beyond that, pricing usually moves into custom enterprise contracts that often start around $30K/year, according to an identity buyer’s guide that pegs Okta at the higher end of the market for organizations that need secure, scalable access across many apps and users (Everykey’s IAM buyer guide). It offers SSO, lifecycle management, adaptive MFA, directory sync (LDAP/AD), and integrates with all major web and mobile frameworks. Integration difficulty is moderate to high: the building blocks are standardized (OIDC, SAML), but there are a lot of knobs.

Standout strengths

• Deep enterprise integrations: Okta CIC connects to LDAP, Active Directory, HR systems, and third-party IdPs, making it a strong fit for hybrid environments with both cloud and legacy apps.
• Unified workforce + customer identity: The same vendor can cover employee SSO and external customer IAM, which simplifies audits and governance in large organizations.
• Mature, flexible IAM: In a comparison of enterprise auth providers, Okta is described as one of the “most flexible and scalable IAM solutions” for multi-vendor environments, highlighting its ability to sit at the center of complex identity architectures (Kinde’s enterprise auth roundup).

“Okta is the most flexible and scalable IAM solution for enterprises that need to integrate with multiple vendors and hybrid environments.” - Top enterprise authentication providers report, Kinde

Watch out for…

• Overkill for small teams: If you’re shipping a solo side project, Okta’s concepts - directory sync, identity brokering, fine-grained policies - are more weight than you need, and the full enterprise pricing is hard to justify.
• Opaque, enterprise-style pricing: After the free/developer tier, you’re usually in “talk to sales” territory, with approvals, security reviews, and annual contracts rather than a simple per-MAU slider.
• Steep learning curve: Getting real value means understanding SAML vs OIDC, just-in-time provisioning, and adaptive MFA policies - not just dropping in an SDK.

Practical example: B2B portal inside a Fortune 500

Picture joining a team that’s building a B2B portal for a global manufacturer. Employees log in with corporate SSO, external partners come in via their own IdPs (Azure AD, Ping, other Okta tenants), and auditors want to see strong MFA and clear access policies. Okta CIC sits in the middle, brokering SSO for each partner, enforcing adaptive MFA for risky actions, and feeding logs to a SIEM. An AI copilot can write the OIDC integration in your Node or Java backend, but it won’t decide which partners need hardware-key MFA for high-value actions, or how to map external groups into your app’s roles.

From a career standpoint, Okta/Auth0 shows up a lot in enterprise job descriptions, especially where security and compliance matter. Getting hands-on with a free developer tenant and wiring a simple app to Okta - while you learn the underlying protocols - signals to hiring managers that you’re comfortable working with the “big kid” car seats used in real corporate fleets, not just the lightweight options for indie apps.

AWS Cognito

AWS Cognito is the no-frills car seat that clips straight into your car’s proprietary rails: if you’re already “driving” an AWS stack, it locks in solidly and rides along cheaply at scale. If you’re not, the installation manual is dense, full of AWS-specific jargon, and easy to misread when you’re just trying to protect your precious cargo without becoming a cloud architect overnight.

Best if…

• You’re heavily invested in AWS already (Lambda, API Gateway, AppSync, Amplify) and want auth that lines up cleanly with IAM and API Gateway authorizers.
• Your priority is low per-user cost at high scale more than polished UX dashboards or drop-in UI components.

Quick facts

• Category: Managed auth as part of the AWS platform
• Pricing: Tiered; independent comparisons estimate roughly $0.0055 per MAU after the free tier, putting a simple 100K-MAU scenario at about $550/month before free allowances are applied (Zuplo’s Cognito vs Auth0 vs Firebase vs Supabase pricing breakdown).
• Features: User pools, social federation, basic MFA, integration with IAM for fine-grained access to AWS resources.
• Frameworks: React via Amplify, Node.js backends, plus native iOS/Android and other SDKs.
• Integration difficulty: Medium to high; configuration involves user pools, identity pools, app clients, and IAM roles, all in AWS-speak.

Standout strengths

• Low cost at scale: Even using the rough $0.0055/MAU figure, Cognito stays in the low hundreds per month around 100K MAUs, which is why it’s frequently called out as the cheapest option among major managed auth providers in high-scale comparisons.
• Tight AWS integration: Tokens from Cognito can be mapped directly to IAM roles and policies, making it straightforward to gate access to S3 buckets, API Gateway endpoints, or AppSync resolvers based on the user’s identity.
• Serverless-friendly: Works naturally with Amplify-generated frontends and Lambda-based backends, which are common in modern, cost-conscious stacks analyzed in guides like MetaCTO’s serverless auth cost breakdown.

Watch out for…

• Configuration complexity: Understanding the difference between user pools and identity pools, and wiring them correctly to API Gateway or AppSync, is a learning curve even for experienced AWS users.
• Console UX and terminology: Compared to something like Clerk or Firebase, Cognito’s console feels dated and packed with AWS-specific concepts that AI can’t fully explain for you.
• Vendor lock-in: While it uses standard tokens (JWT/OIDC), the way you tie Cognito into IAM, API Gateway authorizers, and AppSync means switching later can be as painful as swapping a bolted-in seat across cars.

Practical example: Serverless React app on AWS

Imagine you’re building a React SPA that talks to an API Gateway + Lambda backend and lets users upload files to S3. Cognito user pools handle sign-up/sign-in, Amplify drops in a basic UI, and your Lambdas read Cognito JWTs to decide who can do what. An AI copilot can generate the Amplify setup commands, React hooks, and even sample Lambda authorizer code, but you still need to understand which claims in the token to trust, how to configure redirect URIs safely, and how IAM policies map users to S3 access.

For job hunting, Cognito appears regularly in cloud and DevOps-heavy roles, especially where companies have gone all-in on AWS. Being able to say “I wired Cognito to API Gateway and Lambda, and here’s how I secured it” shows you can work with the heavier, more industrial gear many real-world teams rely on, not just the friendlier SaaS dashboards aimed at early-stage startups.

Keycloak

Keycloak is the industrial-grade car seat that gets bolted straight into the chassis. It’s rugged, self-hosted, and built for serious trips with strict safety rules - think banks, healthcare, or government - but installing and maintaining it means you’re now the mechanic, not just the driver. For many junior devs, that’s overkill for a first app, but it’s exactly what some enterprises and on-prem clients expect.

Best if…

• You need on-premise or private-cloud identity because of regulations, data residency, or strict client policies.
• Your stack already includes Java or Kubernetes, and your team is comfortable running and patching complex services in production.

Quick facts

• Category: Self-hosted open source (Java-based Identity Provider)
• Pricing: Free license; you pay for the servers, storage, and operational overhead.
• Features: SSO, SAML 2.0, OpenID Connect, social login, and user federation with LDAP/Active Directory.
• Frameworks: Language-agnostic via standard protocols (OIDC/SAML); works with most web and mobile stacks.
• Integration difficulty: High - you configure realms, clients, identity brokering, and manage infra yourself, which is why enterprise roundups list it alongside heavier IAM tools in their “for experts only” column (Slashdot’s enterprise authentication software list).

Standout strengths

• Full-featured IdP you control: Keycloak lets you be your own Auth0/Okta-style identity provider, supporting SAML for legacy apps and OIDC for modern ones, plus social logins and custom identity brokering.
• On-prem and private-cloud ready: Ideal when data must stay in a specific region or network, a common requirement in regulated industries that can’t use multi-tenant SaaS.
• Mature and battle-tested: Open-source IAM surveys describe Keycloak as a “heavyweight standard” for Java-based identity providers with SSO and federation capabilities, reflecting its long history in large enterprises.

“Keycloak remains the heavyweight standard for open-source identity providers, especially where enterprises need SSO and federation but can’t rely on SaaS.” - Open-source IAM overview, Cerbos blog

Watch out for…

• Serious DevOps burden: You’re responsible for upgrades, security patches, backups, monitoring, and scaling. That’s more like maintaining your own security system than renting space in someone else’s.
• Steep conceptual curve: Realms, clients, identity brokering, and user federation are powerful but non-trivial. AI can help generate OIDC client code, but it won’t design a safe realm layout or patch CVEs for you.
• Not MVP-friendly: Spinning up Keycloak for a weekend side project is rarely worth it; even Auth0-alternatives guides aimed at startups tend to point people to lighter solutions unless they have explicit on-prem requirements (siit.io’s Auth0 review and alternatives).

Practical example: Regulated healthcare platform

Suppose you join a team building a healthcare platform where all data must live in a private cloud, and hospitals insist on signing in with their existing SAML or OIDC providers. Keycloak runs in your cluster, brokers identity from each hospital’s IdP, and exposes standards-based tokens to your React or Angular frontends and Node/Java backends. AI can scaffold the OIDC clients and some Kubernetes manifests, but you still decide how to isolate realms per tenant, when to require MFA for high-risk actions, and how to roll out upgrades without breaking patient access.

On a resume, “implemented SSO and user federation with Keycloak” signals you’ve dealt with real-world identity complexity, not just pasted SDK snippets. It’s not the first auth “seat” most learners should install, but if you’re aiming at security-heavy, on-prem, or government-style roles, getting comfortable with Keycloak’s straps and buckles can set you apart in a competitive job market.

NextAuth.js / Auth.js

NextAuth.js (now part of the broader Auth.js project) is like the modern, convertible car seat tuned specifically for compact city cars: it snaps perfectly into a Next.js “vehicle,” gives you a lot of adjustability, and doesn’t charge per passenger. For many React/Next learners, it’s the first time auth feels both powerful and understandable instead of buried behind a SaaS dashboard.

Best if…

• You’re building Next.js or other modern SSR/SSG apps and want first-class support for OAuth providers like Google/GitHub plus magic links and credentials.
• You prefer open-source, no per-MAU billing, and are happy to run your own database (Postgres, MySQL, SQLite, etc.).

Quick facts

• Category: Open-source library (ISC/MIT-style licensing)
• Pricing: Free; you pay only for your DB and hosting
• Features: Dozens of OAuth providers, email magic links, credentials auth, rich adapter ecosystem for popular databases
• Frameworks: Primarily Next.js; the Auth.js rebrand is expanding to SvelteKit, SolidStart, and other modern frameworks
• Integration difficulty: Low-to-moderate for Next.js, higher when used outside its “home” framework

Standout strengths

• Perfect fit for Next.js portfolios: It plugs naturally into the Next.js app router, server actions, and SSR, which is why many tutorials and comparisons treat it as the default auth choice for Next-based apps. In a detailed comparison of auth providers, Zsolt Ero describes NextAuth as “the original highly popular and open-source authentication library specifically built to integrate seamlessly with the Next.js framework,” with “high customizability” and support for many providers and adapters.
• No per-user billing: Unlike services that start charging around 10K-50K MAUs, Auth.js stays free as your user count grows, similar in spirit to running your own backend instead of paying per seat like Firebase or Auth0. That’s a big deal when you compare it to per-MAU pricing on platforms like Firebase Auth, where paid plans kick in beyond 50,000 MAUs according to the official Firebase pricing page.
• Great learning curve for real-world OAuth/OIDC: You see providers, callbacks, sessions, and cookies directly in code, which makes concepts like “what happens after the OAuth redirect?” much less mysterious.

“NextAuth.js is the original highly popular and open-source authentication library specifically built to integrate seamlessly with the Next.js framework, offering high customizability and support for a massive number of providers and adapters.” - Zsolt Ero, Comparing Auth Providers

Watch out for…

• You must manage the database: Unlike fully hosted BaaS options, you’re on the hook for provisioning and securing Postgres/MySQL/SQLite and keeping migrations in sync.
• Not a drop-in UI kit: There’s no hosted console or glossy sign-in widget; you build the forms and UX, though there are examples and community components to copy from.
• Web-centric: It shines on the web; for native mobile (especially React Native with deep Firebase integration), other tools may be smoother.

A very practical pattern for a portfolio project is a Next.js SaaS where users sign in with GitHub and Google, and user/session data lives in a cheap Postgres instance. Auth.js handles the providers and sessions in a single route, while your server components call helpers like getServerSession to tailor UI. An AI copilot can generate the config file, provider setup, and even some UI wiring, but you’re still deciding which callback URLs are safe, how long sessions last, and how to secure cookies so tokens never leak into JavaScript-accessible storage.

From a hiring standpoint, Auth.js/NextAuth shows up again and again in React/Node job postings, and there’s even a dedicated community debate on which to pick in resources like the “NextAuth vs Auth.js” comparison video on YouTube. Being able to say “I wired GitHub/Google login into a Next.js app using Auth.js, here’s how I handled sessions and protected routes” demonstrates not just that you can follow a tutorial, but that you understand the underlying straps and buckles of modern web auth well enough to supervise whatever code your AI tools generate.

Auth0

Auth0 (now part of Okta Customer Identity Cloud) is the ultra-adjustable car seat with every lever and cushion you can imagine. It handles social login, B2B SSO, rules, hooks, and complex MFA policies, which is why you see it everywhere in mid-sized and enterprise SaaS. But just like that high-end seat, the more your “kid” grows, the more the price tag starts to matter.

Best if…

• You’re building a B2B or B2C SaaS that needs things like B2B SSO, role-aware MFA, and fine-grained control over login flows.
• Your company either already has, or expects to have, a real auth budget once you move past a prototype.

At a glance, Auth0 is a SaaS authentication platform with a generous free tier and increasingly enterprise-focused paid plans. The free plan typically covers up to 7,500 MAUs with social logins and basic MFA. Above that, the Essentials plan starts around $35/month and adds features like custom domains and stronger MFA, while the Professional tier jumps to roughly $240/month with advanced MFA and machine-to-machine (M2M) auth, according to a detailed Auth0 pricing guide from SaaSworthy. On top of the core features - social login, passwordless options, MFA, and B2B SSO - you also get “Actions,” a serverless-style system for running custom code during auth flows.

Standout strengths

• Enterprise-ready feature set: SAML, OIDC, B2B SSO, and fine-grained MFA policies are first-class, making Auth0 a strong fit when you’re selling into security-conscious customers.
• Powerful extensibility: Actions and rules let you run custom code at signup/login - for example, calling fraud-detection APIs, enriching profiles, or syncing roles to your own database.
• Broad ecosystem and docs: SDKs exist for most common stacks (React, Next.js, Node, mobile, legacy), which is why you’ll see Auth0 mentioned frequently in “Auth0 vs X” comparisons like Supertokens’ Auth0 vs FusionAuth breakdown.

Watch out for…

• Costs that ramp with growth: While 7,500 free MAUs look great early on, once you cross into paid tiers and add advanced MFA or M2M, monthly bills can climb quickly - especially for fast-growing startups.
• Vendor lock-in via customization: The more logic you push into Auth0’s Actions, rules, and metadata, the harder it is to migrate later; you’re tying critical behavior to their platform.
• Overkill for simple apps: For a small side project, wiring Auth0 can feel like strapping a race-car seat into a grocery cart; you’ll carry extra conceptual overhead you don’t really need.

Practical example: Multi-tenant B2B SaaS with SSO

Imagine you’re on a small team building a multi-tenant B2B SaaS. Each customer wants SSO via their own IdP (Okta, Azure AD, others), and security reviewers are asking about MFA, audit logs, and deprovisioning flows. Auth0 lets you model each customer as an organization, plug in their SAML/OIDC connections, and run Actions at login to sync roles and tenant metadata into your app. An AI copilot can generate the React hooks and Node middleware to verify Auth0 tokens, but you’re still responsible for designing the tenant model, deciding when to step up to MFA (for example, on billing changes), and ensuring you can export or migrate user data if pricing ever becomes a problem.

From a career perspective, Auth0/Okta experience shows up in many mid-market and enterprise job postings. Having a portfolio project where you can walk through “here’s how I configured Auth0, here’s how my app trusts its tokens, and here’s how I’d unwind that if we ever had to switch providers” demonstrates not just that you can use a popular tool, but that you understand the tradeoffs behind its straps, buckles, and long-term cost limits.

Firebase Auth

Firebase Auth is the lightweight seat designed for city living: it snaps neatly into mobile and web apps, rides on top of Google’s infrastructure, and gets you on the road fast. If you’re building with React Native, Flutter, or plain JavaScript and don’t want to assemble everything from raw OAuth flows, it can feel like the most straightforward way to get secure sign-in working without becoming a full-time identity engineer.

Best if…

• You’re building mobile-first apps with React Native, Flutter, iOS, Android, or web and want tight integration with Firebase’s other services.
• Your stack already leans on Firebase/Google Cloud (Firestore, Realtime Database, Cloud Functions, FCM) and you’d like auth to plug into that ecosystem with minimal friction.

Quick facts

• Category: Managed auth as part of the Firebase BaaS platform.
• Pricing: On the Spark free tier, you get about 50,000 MAUs for standard providers. On the Blaze plan, you pay roughly $0.0025 per MAU beyond 50K, while SMS for phone auth is billed separately.
• Features: Email/password, phone (SMS) auth, popular social providers, anonymous auth, and support for SAML/OIDC on paid plans.
• Frameworks: Excellent SDKs for Android, iOS, Flutter, React Native, and web.
• Integration difficulty: Generally low: the client SDK and docs are clear, and many tutorials use Firebase as their first auth example.

Standout strengths

• Mobile-optimized SDKs: Firebase Auth is engineered with mobile in mind, which is why it shows up so often in tutorials and comparisons for cross-platform stacks. A pricing comparison from Codehooks’ Supabase vs alternatives guide even uses Firebase as a baseline when discussing the tradeoffs between BaaS options.
• Anonymous and staged onboarding: You can let users start anonymously (great for games or content apps) and then upgrade them to a full account later without losing their data.
• Tight coupling with other Firebase services: The same identity can drive Firestore security rules, Cloud Functions triggers, and FCM notifications, making it easy to build end-to-end features with a single identity layer.

“Firebase Authentication offers a generous free tier for up to tens of thousands of monthly active users, but teams need to carefully monitor SMS usage as phone auth can quickly become the most expensive part of the bill.” - MetaCTO, Complete Guide to Firebase Auth Costs

Watch out for…

• SMS costs and regional pricing: Phone-based auth feels user-friendly, but those OTP texts add up; many teams discover that SMS, not MAUs, dominates their auth bill once they scale.
• Vendor lock-in: Deeply wiring your rules, data model, and functions around Firebase makes later migration harder. You’re effectively tying your auth, database, and hosting to one platform.
• Less suited to complex B2B SSO: While SAML/OIDC support exists on paid plans, Firebase Auth isn’t as focused on enterprise federation and fine-grained policies as tools like Auth0 or Okta.

Practical example: React Native app with phone + social login

Imagine you’re building a React Native app where users sign in with a phone number or a social provider like Google or Apple, and their data lives in Firestore. Firebase Auth handles phone verification, returns ID tokens to your app, and those tokens drive Firestore security rules so users can only read and write their own documents. An AI copilot can scaffold the React Native screens, verification flows, and Firebase initialization for you, but you still have to decide whether to default to phone or email, how strict your Firestore rules should be, and when the rising SMS bill justifies adding a different MFA option.

On the job side, Firebase Auth appears constantly in postings for mobile and cross-platform roles. Being able to say “I built a React Native app using Firebase Auth, here’s how I secured Firestore and managed OTP costs” is a concrete, portfolio-ready story. It also forces you to understand the basics AI can’t decide for you: what an ID token actually is, how client-side rules differ from server-side checks, and where the real limits and hidden costs live in Firebase’s friendly, click-next setup screens - those same limits that only really matter once your app, like that kid in the back seat, starts to grow fast.

Clerk

Clerk is the high-end seat that clicks into ISOFIX in seconds and comes with the padding and cup holders already installed. Instead of just handing you an SDK, it ships full sign-in, sign-up, profile, and organization UIs that drop into your React or Next.js app so you can focus on your product, not reinventing auth screens.

Best if…

• You’re building a modern SaaS with React, Next.js, Remix, or Expo/React Native and you want polished auth UX on day one.
• Your priority is developer experience and time-to-market, and you’re okay paying per MAU once you move beyond the free tier.

Quick facts

• Category: SaaS auth + user management platform.
• Pricing: Free tier with 10,000 MAUs and 100 Monthly Active Organizations (MAOs) included; Pro plan from $25/month plus $0.02 per MAU beyond 10K, as detailed on the official Clerk pricing page.
• Features: Drop-in UI components for sign-in/sign-up, magic links and OTP, MFA, user profiles, organization/teams, webhooks, and session management.
• Frameworks: Deep integrations with Next.js, Remix, React, and Expo/React Native.
• Integration difficulty: Low - you typically import components like <SignIn /> and configure a few environment variables.

Standout strengths

• Drop-in UI that feels production-ready: Instead of designing every screen from scratch, you get composable components for sign-in, sign-up, user profiles, and organization switching that handle edge cases and responsive design for you.
• B2B SaaS built in: Clerk’s organizations and roles model lets you support workspaces and teams without building tenant management from zero - a pattern their own guide on essential user management features for startups calls out as critical for early SaaS teams.
• Dev-friendly DX: Clear docs, TypeScript support, and framework-specific starters make it feel closer to a UI library than a distant identity provider, which is ideal when you’re learning with an AI copilot and want to see working auth flows quickly.

Watch out for…

• Cost at scale: That Pro plan math adds up: at 100K MAUs, the rough estimate is about $1,825/month (90K × $0.02 + $25). That’s reasonable for a funded SaaS, but steep for a hobby project that suddenly takes off.
• SaaS lock-in: Your sessions, org structure, and even some UI expectations are modeled the “Clerk way,” which makes later migration more like swapping an integrated travel system than unplugging a generic seat.
• JS/TS-centric focus: While there are broader SDKs, Clerk’s real sweet spot is the modern JavaScript/TypeScript ecosystem; if your backend world is mostly Java, .NET, or Go, other providers may slot in more naturally.

Practical example: Multi-tenant Next.js SaaS in weeks

Picture shipping a multi-tenant Next.js app where each company gets its own workspace, admins invite teammates, and everyone expects slick login and profile pages. With Clerk, you drop in <SignUp />, <SignIn />, and organization components, wire a bit of Next.js middleware to protect routes, and you’re most of the way there. An AI copilot can generate the boilerplate hooks and middleware, but you still decide your authorization rules inside each org, when to enforce MFA (for example, before billing changes), and how to handle account recovery.

For the job market, Clerk appears more and more in React/Next-focused postings because it lets teams move fast without hiring a dedicated identity specialist. Having a portfolio project where you can walk through “here’s how I used Clerk’s organizations, here’s how my Next.js app trusted its sessions, and here’s how I’d keep costs under control past 10K MAUs” shows employers you can supervise what AI generates, reason about MAU-based pricing, and deliver auth UX that feels like a first-class part of the product instead of an afterthought.

Supabase Auth

Supabase Auth is the convertible car seat that comes bundled with your car: if you’ve already picked Postgres as your “vehicle,” it snaps in cleanly, rides through multiple growth stages, and doesn’t start charging extra the moment your app gets popular. For a lot of JavaScript beginners and career-switchers, it’s the first time auth, database, and storage feel like a single, coherent system instead of a pile of disconnected services.

Best if…

You’re building full-stack apps with Postgres at the core (React, Vue, Svelte, Node, React Native) and you want authentication that’s tightly coupled to your database, with very generous free and low-cost tiers. Supabase Auth sits inside Supabase’s open-source BaaS stack, giving you email/password, social logins, magic links, MFA, and deep Row Level Security (RLS) integration on top of a managed Postgres instance. The official Supabase pricing page calls out a free tier with up to 50,000 MAUs included, and a Pro plan at $25/month that covers up to 100,000 MAUs in one project.

Standout strengths

What makes Supabase Auth stand out is how much it gives you before you ever pull out a credit card, and how directly it plugs into SQL-level security rules instead of hiding access control behind a black box. A detailed “Supabase Review 2026” from Hack’celeration notes that Supabase has become a compelling open-source alternative to Firebase, particularly for teams that want the power of real Postgres with a much clearer, SQL-first security model for their apps (Hack’celeration’s Supabase BaaS review).

• Huge free & low-cost tiers: 50K MAUs free, and 100K MAUs for $25/month on Pro, is extremely competitive when you compare it against providers that start charging hard at 10K-50K MAUs.
• Tight Postgres RLS integration: You can write policies like user_id = auth.uid() directly in SQL so the database itself enforces “a user can only see their own rows,” which is easier to reason about than duplicating rules in multiple services.
• Unified SDK: A single client library handles auth, database queries, storage, and serverless functions, which keeps your React or Node code simpler and easier for AI copilots to scaffold without losing the big picture.
• Open-source core: While you’re likely using the hosted service, the underlying pieces are open-source, which reduces long-term lock-in and gives you an escape hatch if you ever need to self-host.

Watch out for…

The same things that make Supabase Auth appealing can become constraints as your product and company evolve, especially if you move away from relational data or need advanced enterprise identity features. You’re effectively betting that your app will be happy living on Postgres + Supabase for a long time, and that you won’t need extremely complex B2B SSO or identity orchestration that tools like Auth0 or Okta specialize in.

• Postgres-centric model: If your data needs lean heavily toward document or graph storage, the tight auth-DB coupling is less compelling, and moving away later means migrating both auth and data together.
• Auth = DB lock-in: Your auth IDs, RLS policies, and data model are all intertwined; “switching seats as the child grows” is more involved than just swapping an auth provider.
• Less mature enterprise SSO: Supabase supports a wide range of OAuth providers, but complex B2B federation and identity orchestration are still more mature in dedicated IAM platforms.

Practical example: React dashboard with row-level security

Imagine you’re building a React dashboard where each user should only see their own orders. Supabase Auth handles sign-up/sign-in and assigns each user an ID; you then define an RLS policy like using (user_id = auth.uid()) on the orders table. Your React app queries orders directly through the Supabase client, and Postgres quietly enforces that no one can see anyone else’s data. An AI copilot can generate the React components, Supabase client setup, and even example RLS policies, but you’re still the one deciding when to enable MFA in a threat landscape where weak MFA is no longer acceptable, how to design passwordless or magic-link flows that won’t confuse users, and how to test that your RLS really matches your authorization rules. Those decisions - not just the pasted code - are what make Supabase Auth such a valuable learning and portfolio tool for new full-stack developers.

Frequently Asked Questions