rules:
  - id: auth.kotlin.jwt.algorithm-none
    languages:
      - kotlin
    severity: ERROR
    message: |
      A JWT signer or verifier is built with `Algorithm.none()`, the unsecured
      algorithm that produces (and accepts) tokens with no signature. An
      `alg=none` token can be forged by anyone. Changing the subject, roles, or
      expiry costs nothing because there is no signature to verify (CWE-347). This
      is a common AI-generated mistake: the "no signature" algorithm is reached
      for during prototyping or a Ktor demo and never swapped for a real key.

      Sign and verify with a real algorithm and a key from configuration:
      `Algorithm.HMAC256(System.getenv("JWT_SECRET"))` or an RSA/EC key, e.g.
      `JWT.require(Algorithm.HMAC256(secret)).build().verify(token)`.
    # Auth0 java-jwt (com.auth0.jwt): the Algorithm.none() factory, used for both
    # JWT.create().sign(alg) and the JWT.require(alg) verifier.
    pattern-either:
      - pattern: com.auth0.jwt.algorithms.Algorithm.none()
      - pattern: Algorithm.none()
    metadata:
      oauthlint-rule-id: AUTH-KOTLIN-JWT-001
      oauthlint-doc-url: https://oauthlint.dev/rules/kotlin-jwt-algorithm-none
      category: security
      cwe: CWE-347
      owasp: API2:2023
      llm-prevalence: MEDIUM
      technology:
        - java-jwt
        - ktor
      references:
        - https://github.com/auth0/java-jwt
        - https://datatracker.ietf.org/doc/html/rfc8725#section-2.1
        - https://cwe.mitre.org/data/definitions/347.html