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Java Academy · Lesson

JWT: Structure, Creation, and Verification

Manually decode JWT structure, create signed tokens with a secret, and verify claims without frameworks.

What Is a JWT?

JSON Web Token (JWT) is a compact, URL-safe token format for transmitting claims between parties. A JWT is signed (and optionally encrypted). It is self-contained — no database lookup needed to verify claims.

JWT Structure: Header.Payload.Signature

A JWT has three Base64URL-encoded parts separated by dots: header.payload.signature. The header specifies the algorithm. The payload contains claims. The signature verifies integrity.

// Example JWT:
// eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9      <- header
// .eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkFsaWNlIn0  <- payload
// .SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c     <- signature

All lessons in this course

  1. Cryptographic Hashing with MessageDigest
  2. AES Symmetric Encryption
  3. HMAC-SHA256 for Message Integrity
  4. JWT: Structure, Creation, and Verification
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