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JWT validator

Provider-agnostic OIDC JWT validation. Supports RS256/384/512, PS256/384/512, ES256/384/512, EdDSA.

jwt_validator

JWKS-based JWT validation for any standard OIDC provider (Keycloak, Okta, Microsoft Entra ID, Duende, Auth0, …).

The issuer URL's /.well-known/openid-configuration is fetched once and cached; the jwks_uri within it is used to verify token signatures. No provider-specific code — pure OIDC / RFC 7517.

JwtFailReason

Bases: Enum

Why JWT validation failed — used to emit the correct WWW-Authenticate error.

validate_jwt async 

validate_jwt(
    token: str, issuer_url: str
) -> tuple[dict | None, JwtFailReason | None]

Validate a signed JWT via the issuer's JWKS endpoint.

The issuer's /.well-known/openid-configuration is fetched (and cached) to locate the jwks_uri automatically — no need to hard-code a certs URL.

Returns (claims, None) on success. Returns (None, JwtFailReason.EXPIRED) when the token has expired. Returns (None, JwtFailReason.INVALID) for any other failure.

Source code in mcpauthkit/jwt_validator.py 
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async def validate_jwt(token: str, issuer_url: str) -> tuple[dict | None, JwtFailReason | None]:
    """
    Validate a signed JWT via the issuer's JWKS endpoint.

    The issuer's /.well-known/openid-configuration is fetched (and cached)
    to locate the jwks_uri automatically — no need to hard-code a certs URL.

    Returns (claims, None) on success.
    Returns (None, JwtFailReason.EXPIRED) when the token has expired.
    Returns (None, JwtFailReason.INVALID) for any other failure.
    """
    try:
        header = jwt.get_unverified_header(token)
        alg = header.get("alg", "RS256")
        if alg not in _ALLOWED_ALGORITHMS:
            logger.warning("JWT uses disallowed algorithm: %s", alg)
            return None, JwtFailReason.INVALID

        oidc = await _get_oidc_config(issuer_url)
        jwks = await _get_jwks(oidc["jwks_uri"])

        claims = jwt.decode(
            token,
            jwks,
            algorithms=list(_ALLOWED_ALGORITHMS),
            options={"verify_aud": False},
        )

        # Enforce issuer
        expected_issuer = oidc.get("issuer", "")
        if expected_issuer and claims.get("iss") != expected_issuer:
            logger.warning(
                "JWT issuer mismatch: expected '%s', got '%s'",
                expected_issuer,
                claims.get("iss"),
            )
            return None, JwtFailReason.INVALID

        return claims, None

    except ExpiredSignatureError:
        logger.debug("JWT validation failed: token expired")
        return None, JwtFailReason.EXPIRED
    except JWTError as exc:
        logger.debug("JWT validation failed: %s", exc)
        return None, JwtFailReason.INVALID
    except Exception as exc:
        logger.warning("Unexpected error during JWT validation: %s", exc)
        return None, JwtFailReason.INVALID