A Developer's Essential Guide What is JWT?
JSON Web Token (JWT) is a compact, URL-safe token format used for securely transmitting information between parties.
Think of it as a digital passport that carries user credentials and claims in a standardised, verifiable format.
🔄 JWT Workflow:
1️⃣ Login Request → User provides credentials
2️⃣ JWT Issued → Server validates and responds with a token
3️⃣ Client Stores JWT → Usually in localStorage or sessionStorage
4️⃣ Authenticated Requests → JWT is sent in Authorisation: Bearer
5️⃣ Server Verifies & Responds
How is JWT Created?
A JWT consists of three parts separated by dots (.):
🔹 Header: Contains token type (JWT) and signing algorithm (e.g., HS256, RS256)
🔹 Payload: Contains claims (user data, permissions, expiration)
🔹 Signature: Ensures token integrity using a secret key or certificate
Structure: header.payload.signature
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkFua2l0IiwiaWF0IjoxNjg4MDA2NDc1fQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c 🔍 JWT Payload Breakdown (Middle Part):
This is a Base64-encoded JSON and may look like this:
{ "sub": "1234567890", // Subject (user ID) "name": "Ankit", // User name "iat": 1688006475, // Issued At (timestamp) "exp": 1688010075, // Expiration time (optional) "role": "admin" // Custom claim } Payload Information:
The payload contains "claims" - statements about the user and
additional data:
• Registered Claims: Standard fields like iss (issuer), exp (expiration), sub (subject)
• Public Claims: Custom fields defined in JWT registry
• Private Claims: Application-specific data like user roles, permissions
Key Benefits:
✅ Stateless: No server-side session storage needed
✅ Scalable: Perfect for micro services and distributed systems
✅ Secure: Cryptographically signed and optionally encrypted
✅ Cross-platform: Works across different domains and applications
Important Considerations:
⚠️ Size: JWTs can become large with extensive payload data
⚠️ Security: Never store sensitive data in payload (it's Base64 encoded, not encrypted)
⚠️ Expiration: Always set appropriate expiration times
⚠️ Storage: Store securely (httpOnly cookies preferred over localStorage)
Common Use Cases:
🎯 Authentication and authorization
🎯 Single Sign-On (SSO)
🎯 API security
🎯 Information exchange between services
Pro Tips: 💡 Use short expiration times with refresh tokens 💡 Implement proper token revocation strategies 💡 Always validate tokens on the server side applications?
Share your experiences below! 👇
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