JWT vs. Session Authentication: Which is Best?

Comparing ID Card Types: Session vs. JWT

This article compares two common types of ID cards used for user authentication: Session-based and JWT (JSON Web Token)-based. Understanding the differences between these methods is crucial for choosing the right approach for your application.

The Problem: HTTP is Stateless

HTTP, the foundation of the web, is a stateless protocol. This means that each request from a user is treated as a completely new and independent event. After a user logs in, subsequent requests don't automatically "remember" that the user is authenticated. Therefore, we need a mechanism to identify users across multiple requests.

Session-Based Authentication

Login Process

1. The user submits their username and password to a login interface.
2. The server verifies these credentials against a database.

3. Upon successful authentication, the server creates a session. This involves:

   • Generating a unique random string, called the session ID.

   • Storing user information (user ID, username, etc.) in a data store like Redis, with the session ID as the key.

   • The server returns the session ID to the client.
   • The client (typically a browser) stores the session ID, usually as a cookie.

Accessing Restricted Resources

1. When the user attempts to access a resource requiring authentication, the browser automatically includes the cookie containing the session ID in the request header.
2. The server extracts the session ID from the request header.
3. The server uses the session ID to query Redis and retrieve the corresponding user information.
4. If the user information is found, the server confirms the user's authenticated status and proceeds with the request.

Session Expiration

When writing to Redis, a time-to-live (TTL) or expiration time is set for the session data (e.g., 30 days). After this period, the session ID becomes invalid, requiring the user to log in again.

Session-Based Authentication Characteristics

• Dependency on Redis: Requires deploying and maintaining a Redis instance or similar data store to store session data.

• Increased Latency: Each request to a protected resource requires a read operation from Redis, adding latency.

• Scalability Concerns: High traffic can strain Redis, potentially becoming a bottleneck. While Redis is very fast, the extra network hop may become an issue.

• Easy Revocation: Revoking a user's access is simple; just delete the corresponding session ID from Redis. This is useful when an account is compromised.

JWT-Based Authentication

Login Process

1. The user provides their username and password.
2. The server verifies the credentials.

3. If successful, the server generates a JWT. This involves:

   • Creating a JSON header and a JSON payload containing claims (user information, expiration time, etc.).

   • Generating a signature based on the header, payload, and a secret key using an algorithm.

   • Combining the header, payload, and signature into a single, encoded string – the JWT.

   • The server sends the JWT to the client.
   • The client stores the JWT locally, often as a cookie.

Accessing Restricted Resources

1. When accessing a protected resource, the client includes the JWT in the request header (usually in the Authorization header).
2. The server receives the JWT and validates it.
3. The server validates the signature by re-generating the signature from the header and payload using the secret key. This ensures the token hasn't been tampered with. The server also checks the expiration claim in the payload to ensure the token is still valid.
4. If the signature is valid and the token hasn't expired, the server extracts user information from the payload and authorizes the request.

JWT-Based Authentication Characteristics

• Stateless on the Server: The server doesn't need to store any session information. The user's authentication data is self-contained within the JWT.

• Faster Performance: No need to query a database or data store for each request, reducing latency. This is because you don't have to read from a database like Redis.

• Difficult Revocation: It's challenging to revoke a JWT before its expiration date, as the server doesn't track individual tokens.

• CPU Intensive: Signature verification requires cryptographic operations, which can be CPU-intensive.

• Security Considerations: The payload is base64 encoded, not encrypted, so it shouldn't contain sensitive information. Consider using HTTPS to encrypt the entire request. If you must store sensitive information, encrypt the payload before creating the JWT.

• HTTPS Requirement: Using HTTPS is crucial, because browsers may transfer cookies (containing the JWT) to the service end when requesting all interfaces, and this transfer could be exposed to the Internet.

Conclusion

Both Session and JWT-based authentication have their strengths and weaknesses. Session-based authentication offers easier revocation and more flexibility for storing user data but requires a server-side data store and can introduce latency. JWT-based authentication provides statelessness and faster performance, but revocation is more difficult, and sensitive data shouldn't be stored directly in the token. Choose the method that best fits your specific application requirements and security considerations.