Authentication in REST APIs

// Structure: header.payload.signature, all base64-encoded
// Example payload (decoded):
{
  "sub": "user_42",       // subject (user id)
  "role": "admin",
  "iat": 1716777600,       // issued at (unix time)
  "exp": 1716781200,       // expires at (1 hr later)
  "iss": "myapp.com"       // issuer
}

// Server signs the payload with a secret. Client cannot tamper without invalidating the signature.
// On each request:
Authorization: Bearer eyJhbGciOiJIUzI1NiIs...

// Server verifies signature + expiry; trusts the payload.
// Pros: stateless (no DB lookup per request).
// Cons: can't revoke before expiry without a denylist (which defeats statelessness).

// npm i jose
import * as jose from 'jose';

const secret = new TextEncoder().encode(process.env.JWT_SECRET!);

// Sign
const token = await new jose.SignJWT({ sub: 'user_42', role: 'admin' })
  .setProtectedHeader({ alg: 'HS256' })
  .setIssuedAt()
  .setExpirationTime('1h')
  .setIssuer('myapp.com')
  .sign(secret);

// Verify
try {
  const { payload } = await jose.jwtVerify(token, secret, {
    issuer: 'myapp.com',
  });
  // payload.sub, payload.role available
} catch (e) {
  // expired or tampered
}