Auth.js is an open-source library for authentication that is specifically tailored to work effortlessly with contemporary JavaScript frameworks, delivering a secure and adaptable authentication solution. It accommodates a variety of authentication options, such as OAuth (including services like Google and GitHub), user credentials, and WebAuthn, giving developers the freedom to select the best method for their applications. This library is versatile enough to be used with several frameworks, including Next.js, SvelteKit, Express, Qwik, and SolidStart, which allows for straightforward implementation of authentication features across diverse platforms. Additionally, Auth.js includes integrated support for widely-used databases such as Prisma, Drizzle ORM, Supabase, Firebase, and TypeORM, streamlining user data management processes. To enhance security, it incorporates features like signed cookies, CSRF token protection, and encrypted JSON Web Tokens (JWTs), all designed to safeguard user information effectively. Furthermore, Auth.js is optimized for performance in serverless environments and comes with extensive documentation and practical examples to assist developers in getting started. This library not only simplifies authentication but also ensures that applications remain secure and user-friendly.