Identity Geek Speak: Session Tokens – what are they?

Wondering how session management works in web applications? Curious about how session tokens maintain user context and state in a stateless environment like the web? You’re in the right place! In this article, we'll explore session tokens, their use in maintaining the state of user sessions, and the potential security risks associated with their use.

Unmasking Session Tokens

Let's start with the fundamentals. What exactly is a session token? In simple terms, a session token is a unique identifier that is generated and sent from the server to the client after successful authentication. It can maintain the user's state and track their activities during a session.A session token essentially bridges the stateless nature of HTTP protocols, remembering user-specific data across multiple requests. Unlike JWT tokens, session tokens don't contain any intrinsic user data or information. Instead, they act as a reference ID that the server can use to fetch user-specific data stored on the server side.

Building Blocks of Session Tokens

Let's dissect a typical session token system:

• Session Token: This is the unique identifier generated for each new session. Upon successful user authentication, it is created on the server-side and sent to the client. The client will send this token with each subsequent request to maintain the session.

• Session Store: This is where session data is kept on the server-side. Each session token corresponds to a specific set of session data in the store. This data includes user identity, preferences, and other context-specific data.

• Cookie: Typically, session tokens are sent to the client as HTTP cookies. When a user logs in, the server creates a session, stores the session data, generates a session token, and sends it to the client as a Set-Cookie header in the HTTP response. The browser stores this cookie and sends it to the server with each subsequent HTTP request.

Example

Now, let's imagine you're developing a web application called "Superb Site". You've implemented a session-based authentication using a server-side session store. Here's what happens when a user tries to log in to your site:

1. The user navigates to "Superb Site" and enters their login credentials.
2. Upon successfully validating the credentials, "Superb Site" creates a new session on the server. This session holds data such as the user's ID, their preferences, and more.
3. "Superb Site" then generates a unique session token corresponding to the newly created session and sends it back to the client's browser as an HTTP cookie.
4. The client's browser receives the session cookie, which contains the session token, and stores it.
5. The browser automatically includes the session cookie in the HTTP request header with each subsequent request.
6. Upon receiving the request, "Superb Site" extracts the session token from the cookie, looks up the corresponding session data in the session store, and uses that data to maintain the user's state.
7. If the user logs out or after a predetermined timeout period, "Superb Site" invalidates the session on the server, and the client's browser discards the corresponding cookie.

Security Considerations

Like any authentication method, using session tokens presents its own set of security considerations. Here are a few of the most significant ones:

• Session Hijacking: If an attacker manages to steal a session token (for example, via an insecure connection), they can impersonate the user. To mitigate this risk, always use HTTPS connections and consider additional security measures like setting the HttpOnly flag on your session cookies to prevent access from client-side scripts.
• Session Fixation: This attack involves an attacker providing a potential victim with a link that includes a specific session ID. The victim logs in, and the attacker can now use the previously known session ID to access the session. Mitigation strategies include regenerating the session ID after login and invalidating the old session ID.
• Cross-Site Scripting (XSS): XSS attacks can steal session cookies if the session tokens are not properly secured. Set the HttpOnly flag on your session cookies and consider other measures like Content Security Policies (CSP) to mitigate XSS risks.
• Cross-Site Request Forgery (CSRF): CSRF attacks trick the victim into submitting a malicious request with the victim's session token, thereby impersonating the victim. Implementing CSRF tokens is a common mitigation strategy for such attacks.

Session Token vs. JWT

CriteriaJWTSession TokenBandwidth UsageHigher. The size of a JWT can be larger because it includes user data and signatures.Lower. Session tokens are usually short and don't include user data.CPU UsageHigher. The server must verify the JWT signature and decode the token on every request.Lower. The server needs to look up the session ID in the session store.ScalabilityBetter for stateless, distributed systems (like microservices) as JWTs don't require a central session store.Can be more challenging to scale as session tokens require a centralized session store.Data PrivacyData in JWTs can be read by anyone who has the token, so sensitive data shouldn't be stored in a JWT.Data associated with a session token is stored server-side and isn't exposed to the client.RevocationMore difficult. There's no easy way to revoke a JWT before it expires.Easier. The server can remove the session ID from the session store to invalidate it.ExpiryCan set a specific expiry time in the JWT itself.Expiry time can be set when creating the session and stored on the server side.Cross-Domain RequestsEasier to handle cross-domain requests as the JWT is included in the HTTP header.Can be complicated by browser same-origin policies, but can be handled with CORS settings.

Conclusion

Session tokens, when implemented and managed correctly, provide an efficient way to maintain user state in your applications. While they have their own set of security considerations, these can be mitigated with good security practices and diligent application design.Stay tuned for more, and keep those questions coming!