Authentication is how an application identifies who the user is.
Two widely used approaches are session-based authentication and token-based authentication. While both achieve the same goal, they differ in storage, scalability, and security trade-offs.
TL;DR
• Session-based: Server stores sessions, simple, vulnerable to CSRF, great for traditional web apps
• Token-based: Client stores tokens, stateless, scalable, watch out for XSS, perfect for APIs and SPAs
Session-Based Authentication
Session-based authentication is the traditional approach used in many web applications.
When a user logs in, the server creates a session and stores user data on the server. A cookie containing the session ID is sent to the browser. The browser automatically includes this cookie with every request, allowing the server to recognize the user.
Advantages
• Easy to implement and understand
• Simple login and logout flow
• Works well for traditional server-rendered applications
Limitations
• Requires server-side session storage
• Harder to scale in distributed systems
• Vulnerable to CSRF attacks, since cookies are automatically sent by the browser
Token-Based Authentication
Token-based authentication is commonly used in modern applications.
After successful login, the server issues a token (often a JWT). The client stores this token and sends it with each request, usually in the Authorization header. The server validates the token without storing any session data.
Advantages
• Stateless and highly scalable
• Well-suited for APIs, mobile apps, and SPAs
• Works smoothly in microservices architectures
Limitations
• Tokens stored in localStorage are vulnerable to XSS attacks
• Logout and token revocation are more complex
To improve security, tokens can also be stored in HttpOnly cookies, which prevents access from JavaScript and helps reduce XSS risks. However, because cookies are sent automatically, this approach may again require CSRF protection.
Storage and Security Trade-Offs
Security largely depends on where authentication data is stored.
• Sessions stored in cookies
Cookies are automatically sent with requests, which makes applications more vulnerable to CSRF attacks. Using HttpOnly and Secure flags helps reduce other risks.
• Tokens stored on the client
Tokens stored in localStorage are not automatically sent, reducing CSRF risk, but they are exposed to XSS if malicious scripts run in the browser.
Each approach involves a balance between convenience, scalability, and security.
Conclusion
There is no one-size-fits-all solution.
Session-based authentication is a solid choice for traditional web applications, while token-based authentication is better suited for modern, scalable, API-driven systems. Choosing the right approach—and securing it properly—is what truly matters.
