JWT vs session strategy in NextJS - Visual Side-by-Side Comparison

Concept Flow - JWT vs session strategy

User logs in

↓

Server verifies credentials

↓

Create JWT token

↓

Send JWT to client

↓

Client stores JWT

↓

Client sends JWT

↓

Server verifies JWT

↓

Access granted or denied

↓

Logout clears JWT or session

This flow shows how user login leads to either JWT token creation or server session creation, how the client stores and sends them, and how the server verifies them for access.

Execution Sample

NextJS

async function login(req, res) {
  const { username, password } = req.body;
  if (validUser(username, password)) {
    const token = createJWT(username);
    res.json({ token });
  } else {
    res.status(401).end();
  }
}

This code logs in a user, creates a JWT token if valid, and sends it to the client.

Execution Table

Step	Action	Input/State	Output/State Change	Notes
1	Receive login request	username='alice', password='1234'	Request received	Start login process
2	Validate credentials	Check username and password	Valid user	Credentials match
3	Create JWT token	username='alice'	JWT token created	Token contains user info
4	Send token to client	JWT token	Client receives token	Client stores token locally
5	Client sends token with request	JWT token in header	Server receives token	Token used for auth
6	Server verifies token	JWT token	Token valid	Access granted
7	Logout	Client deletes token	Token invalidated client-side	Session ends
8	Session strategy alternative	User logs in	Server creates session and cookie	Session stored server-side
9	Client sends cookie	Session cookie	Server checks session	Access granted if session valid
10	Logout	Client deletes cookie	Session destroyed server-side	Session ends

💡 Process ends after logout or failed validation

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 6	Final
username	undefined	'alice'	'alice'	'alice'	'alice'	undefined
password	undefined	'1234'	'1234'	'1234'	'1234'	undefined
validUser	false	true	true	true	true	false
token	undefined	undefined	'jwt_token_string'	'jwt_token_string'	'jwt_token_string'	undefined
session	undefined	undefined	undefined	undefined	undefined	session object or undefined

Key Moments - 2 Insights

Why does JWT store user info on the client while sessions keep it on the server?

JWT tokens are self-contained and include user info, so the server just verifies the token signature (see execution_table step 3 and 6). Sessions store data on the server, so the client only holds a session ID cookie (see step 8 and 9).

What happens if the JWT token is stolen?

Since JWT is stored client-side and sent with requests (step 5), if stolen, it can be used until it expires. Sessions can be invalidated server-side immediately (step 10), offering more control.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the JWT token created?

A Step 3

B Step 2

C Step 5

D Step 8

💡 Hint

Check the 'Action' column for 'Create JWT token'

According to variable_tracker, what is the value of 'validUser' after step 2?

A false

B true

C undefined

D 'jwt_token_string'

💡 Hint

Look at the 'validUser' row under 'After Step 2'

If the client deletes the JWT token, what happens next according to the flow?

A Server creates a new token automatically

B Session is destroyed server-side

C Access is denied on next request

D Client sends session cookie instead

💡 Hint

Refer to concept_flow step 'Logout clears JWT or session'

Concept Snapshot

JWT vs Session Strategy

- JWT stores user info in a token sent to client.
- Sessions store user info on server, client holds session ID cookie.
- JWT verification is stateless; sessions require server memory.
- JWT tokens expire; sessions can be destroyed anytime.
- Choose JWT for scalability; sessions for control and security.

Full Transcript

This visual execution compares JWT and session strategies in Next.js authentication. The flow starts with user login, then either a JWT token is created and sent to the client, or a session is created and stored on the server with a cookie sent to the client. The client stores and sends these tokens or cookies with requests. The server verifies JWT tokens by checking their signature, or checks sessions by looking up stored data. Logout clears tokens or sessions. The execution table traces each step from login to logout, showing state changes. The variable tracker follows key variables like username, password, validUser, token, and session through the process. Key moments clarify why JWT stores info client-side while sessions keep it server-side, and the security implications if tokens are stolen. The quiz tests understanding of when tokens are created, variable states, and logout effects. The snapshot summarizes the main differences and use cases for JWT and sessions.