Fix JWT Vulnerabilities (Weak Signing, None Algo) in RedwoodJS

RedwoodJS auth decoders are the gatekeepers of your GraphQL API. If you are rolling a custom JWT decoder or misconfiguring the underlying 'jsonwebtoken' library, you are likely vulnerable to algorithm switching attacks (alg: none) or secret brute-forcing. In a RedwoodJS environment, this usually happens in 'api/src/lib/auth.js'. Stop trusting the header; start enforcing the spec.

The Vulnerable Pattern

// api/src/lib/auth.js
import jwt from 'jsonwebtoken'
export const authDecoder = async (token, type) => {
if (type !== ‘custom’) return null
// VULNERABILITY 1: Weak, hardcoded secret
// VULNERABILITY 2: No algorithm enforcement (allows ‘alg: none’ or HMAC vs RSA confusion)
return jwt.verify(token, ‘secret-key’)
}

The Secure Implementation

To secure RedwoodJS JWT handling, we implement three critical layers. First, Algorithm Whitelisting: by passing 'algorithms: ["HS256"]' into the verify options, we explicitly instruct the library to reject tokens using 'alg: none' or any unexpected asymmetric keys. Second, Secret Entropy: we move the secret to an environment variable and validate its length to prevent offline brute-force attacks. Third, Claims Validation: we enforce 'issuer' and 'audience' checks to ensure the token was intended for our specific API and environment, preventing token replay across different services.

// api/src/lib/auth.js
import jwt from 'jsonwebtoken'
export const authDecoder = async (token, type) => {
if (type !== ‘custom’) return null
const secret = process.env.JWT_SECRET
if (!secret || secret.length < 32) {
throw new Error(‘Critical Security Error: Weak or missing JWT_SECRET’)
}
try {
return jwt.verify(token, secret, {
algorithms: [‘HS256’], // Explicitly whitelist the algorithm to block ‘none’
issuer: ‘your-app-domain’,
audience: ‘your-app-api’
})
} catch (e) {
throw new Error(‘Invalid or expired token’)
}
}