Absolutely!
Here's a comprehensive write-up on JWT Authentication that you can copy into
a Word document:
JWT Authentication: A Secure Token-Based System
Introduction
JWT (JSON Web Token) is an open standard (RFC 7519) used for securely transmitting
information between parties as a JSON object. It is widely used in modern web applications
for authentication and authorization due to its simplicity, statelessness, and compact
format.
JWTs are digitally signed, which means their authenticity and integrity can be verified.
How JWT Works
1. User Logs In
o The user sends their credentials (username and password) to the server.
2. Server Verifies Credentials
o If valid, the server generates a JWT and sends it back to the client.
3. Client Stores the Token
o The client (usually a web or mobile app) stores the token, typically in
localStorage or sessionStorage.
4. Client Sends Token with Requests
o On every subsequent request to protected resources, the token is sent in the
HTTP Authorization header:
o Authorization: Bearer <token>
5. Server Verifies the Token
o The server checks the signature and validity of the token to determine access
rights.
Structure of a JWT
A JWT is composed of three parts, separated by dots (.):
xxxxx.yyyyy.zzzzz
Header.Payload.Signature
1. Header
o Specifies the signing algorithm and token type.
2. {
3. "alg": "HS256",
4. "typ": "JWT"
5. }
6. Payload
o Contains claims or user-specific data.
7. {
8. "sub": "1234567890",
9. "name": "John Doe",
10. "admin": true,
11. "exp": 1631901630
12. }
13. Signature
o Ensures the token wasn’t tampered with.
14. HMACSHA256(base64UrlEncode(header) + "." +
base64UrlEncode(payload), secret)
Types of Claims in JWT
Registered Claims: Predefined (e.g., iss, exp, sub, aud)
Public Claims: Can be defined by those using JWTs
Private Claims: Custom claims agreed upon by sender and receiver
JWT Authentication vs. Session Authentication
Feature JWT Sessions
Storage Client-side (e.g., browser) Server-side
Stateless Yes No
Scalability High Requires session store
Cross-domain support Good Limited
Token Revocation Harder Easier
Security Best Practices
1. Use HTTPS: Always use HTTPS to prevent token interception.
2. Set Expiry (exp): Keep tokens short-lived to limit the damage of leaks.
3. Store Tokens Securely: Avoid localStorage if you’re concerned about XSS.
4. Use Refresh Tokens: Implement a refresh token mechanism to re-issue access
tokens.
5. Blacklist Tokens on Logout: If necessary, maintain a blacklist for invalidated tokens.
6. Validate Token on Every Request: Never trust input from the client.
Common Use Case Flow
1. Login:
o User sends POST /login with credentials.
o Server responds with a JWT.
2. Access Protected Resource:
oUser sends GET /profile with JWT in the Authorization header.
oServer verifies the token and returns the data.
3. Token Expiration:
o When expired, client uses a refresh token (if implemented) to get a new one.
4. Logout:
o Client deletes the token. Server may blacklist the token if stored.
Example JWT Token
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.
eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.
SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
Conclusion
JWT Authentication is a powerful and scalable method for securing APIs and applications. Its
stateless nature reduces server-side overhead, making it ideal for modern distributed systems,
microservices, and mobile applications. However, it must be used with care and proper
security practices to ensure user data remains safe.
