React and Next.js are popular frameworks for building dynamic web applications, each offering distinct approaches to user authentication. React, a JavaScript library developed by Facebook, excels in creating reusable UI components for single-page applications and uses client-side rendering (CSR) by default, necessitating a more customized approach to secure user authentication. Conversely, Next.js, built on React, provides enhanced performance with server-side rendering (SSR), static site generation, and built-in routing and API capabilities, making it more suitable for projects that prioritize development speed, SEO, and security. While React offers extensive flexibility for complex authentication requirements using third-party libraries, Next.js streamlines the process with its structured approach and built-in features. Descope is introduced as a framework-agnostic tool that simplifies authentication implementation across both frameworks by offering prebuilt, customizable flows and reducing development time. Ultimately, the choice between React and Next.js depends on the project's complexity, the team's expertise, and the specific needs concerning SEO, initial load times, and authentication security.