Google's Firebase is an entire app development platform that's packed with features.It comes with storage, cloud functions, monitoring and, of course, user authentication. The free tier comes with 50,000 MAUs. Beyond that pricing start at $0.0055/MAU and goes down to as low as $0.0025/MAU as you scale to millions of users. Firebase authentication supports email and password auth, phone auth, magic links, two-factor authentication and social identity providers - mainly Google, Google Play Games, Facebook, Apple, Microsoft, Twitter, GitHub and OAuth access tokens.

Auth0 is an identity and access management (IAM) platform designed to simplify authentication and authorization for applications. It provides a flexible solution that allows developers to implement secure login systems without having to build them from the ground up. Auth0 supports various authentication methods, including username-password credentials, social logins (like Google, Facebook, and GitHub), enterprise identity providers (such as Active Directory and SAML-based systems), and passwordless options. The platform is highly adaptable, offering over 30 software development kits (SDKs) that cater to a wide range of languages and frameworks—JavaScript, Python, .NET, iOS, Android, and more. This makes integration straightforward regardless of the tech stack. Beyond basic authentication, Auth0 offers advanced features like multi-factor authentication (MFA), single sign-on (SSO), and fine-grained authorization. These tools enable organizations to enforce complex access control policies, supporting both role-based (RBAC) and attribute-based (ABAC) models. Auth0 also addresses enterprise needs through features like user provisioning, directory synchronization, and support for B2B, B2C, and B2E use cases. It’s designed with scalability in mind, making it suitable for both startups and large enterprises. The platform’s extensibility allows developers to customize authentication flows, implement rules for conditional access, and integrate third-party services. Since its acquisition by Okta, Auth0 operates as a product unit under the Okta umbrella, complementing Okta’s broader suite of identity solutions while maintaining a developer-first focus. This combination brings together Okta’s enterprise-grade security with Auth0’s developer-centric approach, offering a comprehensive solution for modern identity challenges.

Clerk is a comprehensive user management and authentication platform designed to streamline how developers handle user accounts within web and mobile applications. It offers a suite of embeddable UI components—such as <SignIn/>, <SignUp/>, <UserButton/>, and <UserProfile/>—that integrate seamlessly into your application without redirecting users off-site. These components are fully customizable to match your brand, making the user experience cohesive and frictionless. Under the hood, Clerk provides a robust API and SDKs compatible with modern frameworks like Next.js, Remix, React, and Expo. It handles the entire authentication lifecycle, supporting multifactor authentication (MFA), session management, passwordless sign-in (via magic links or one-time passcodes), and traditional password-based methods with breach detection. The platform also integrates social sign-on (SSO) with over 20 providers, enabling quick user onboarding while adhering to security best practices. Clerk’s security posture includes SOC 2 Type 2 certification and CCPA compliance, with continuous third-party audits and penetration testing. Fraud prevention measures, like disposable email blocking and bot detection powered by machine learning, are built-in to reduce spam and abusive sign-ups. For B2B SaaS applications, Clerk provides advanced multi-tenancy features, enabling organization-based user management with custom roles, permissions, auto-join functionality based on email domains, and invitation systems—all accessible through both code and an admin dashboard. Developers benefit from rapid integration, significantly reducing the time spent on building authentication systems from scratch. Clerk acts as the single source of truth for user data and integrates seamlessly with popular backend services like Supabase, Firebase, and Convex. With free access for up to 10,000 monthly active users, it’s positioned as a scalable solution that grows with your application’s needs.

Supabase is the open-source alternative to Firebase. Like Firebase, it's a complete app development platform with user authentication, cloud functions, APIs, Postgres database, storage, vector embeddings, and other features. Supabase projects come with PostgreSQL's policy engine for fine-grained user access rules. It has social login integrations with Google, Facebook, GitHub, Azure (Microsoft), Gitlab, Twitter, Discord, and many more. They offer a customizable authentication component for React. Phone login and MFA can be added through third-party SMS providers such as Twilio or Bird. The free tier comes with 50,000 monthly active users. The Pro plan, at $25/month, comes with 100,000 MAUs and $0.00325/MAU beyond that.

Stytch provides a suite of tools designed to simplify authentication, authorization, and security for web and mobile applications. If you're developing an app and need a way for users to log in—whether with passwords, passkeys, or entirely passwordless methods—Stytch offers APIs and SDKs that handle these complexities. Their focus is on making authentication seamless for both developers and end-users while ensuring high security standards. For businesses, particularly B2B SaaS companies, Stytch enables advanced features like multi-tenancy, role-based access control (RBAC), and single sign-on (SSO). They provide an embeddable admin portal, allowing enterprise customers to manage their own authentication configurations, organizational settings, and integrations with identity providers—without constant developer involvement. Stytch places a strong emphasis on scalability and flexibility. Their tools are designed to “just work” across a range of use cases, from simple consumer apps to complex enterprise platforms. Developers can choose how much of the authentication flow they want to control—using pre-built UI components for quick implementation or leveraging headless SDKs and backend APIs for a fully customized experience. Security and fraud prevention are also core to Stytch’s offering. They provide real-time bot detection, device-aware multi-factor authentication, and intelligent rate limiting to protect against credential stuffing and other forms of account abuse. Their infrastructure ensures that login codes and authentication requests are delivered reliably, even when SMS or email providers fail. Stytch supports a broad range of programming languages and frameworks, including Python, Node.js, Java, React, and iOS, making integration into existing tech stacks straightforward. Their platform is designed for developers who want to build secure, user-friendly authentication systems without reinventing the wheel.

Ory is an API-first identity manager. They offer authentication, analytics, access control, machine-to-machine authentication and more. They have SDKs for the major languages: - Dart - .NET - Elixir - Go - Java - JavaScript - PHP - Python - Ruby - Rust Unfortunately, they don't offer a free tier. Pricing starts at $29/month and includes 1,000 daily active users. Then it's $30 / 1,000 additional DAUs.

Appwrite is an open-source platform for building scalable applications. It comes with authentication, databases, storage, and functions. It's basically a complete development platform. They have an extremely generous free plan with 75,000 MAUs free of charge and their Pro plan is only $15/month. Appwrite offers email and password login, phone auth, magic links, email OTP, anonymous login, JWT login, SSR login, custom tokens, and two-factor authentication.

Formerly known as NextAuth. It's is an open-source authentication library originally built for NextJS. Auth.js is free to use and comes with over 80 integrations for various third-party identity providers such as Google, Facebook, Auth0, Apple etc. You can use it with your own database if you choose to. It works with MySQL, Postgres, MSSQL and MongoDB. Auth.js is compatible with Next.js, SvelteKit and SolidStart as of March 2024.

Keycloak is an open source identity and access management solution. It supports Keycloak single-sign-on and OpenID Connect or SAML 2.0 Identity Providers (Google, Facebook, GitHub etc).

Gluu offers various authentication solutions based on open-source software. There is a self-hosted solution, a managed solution, and a free fully open-source solution based on the Linux Foundation Janssen Project.

Lucia is an open source auth library that abstracts away the complexity of handling sessions. It works with any JS runtime - Node.js, Bun, Deno, Cloudflare Workers. It's also fully typed. It integrates with MongoDB. PostgreSQL, MySQL, SQLite, and with their respective ORMs and query builders.

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