Function _derive_session_fernet

web/pgadmin/utils/session.py:81–112

Derive a Fernet instance from `SECRET_KEY` for session-body confidentiality. Layer 1 of the on-disk session protection. The HMAC header (added in PR 1) protects integrity of the on-disk bytes; this Fernet layer additionally protects confidentiality so that a leak of `sessions/`

(secret)

def _derive_session_fernet(secret):
    """Derive a Fernet instance from `SECRET_KEY` for session-body
    confidentiality.

    Layer 1 of the on-disk session protection. The HMAC header (added in
    PR 1) protects integrity of the on-disk bytes; this Fernet layer
    additionally protects confidentiality so that a leak of `sessions/`
    files alone (without the SECRET_KEY in `pgadmin4.db`) does not
    expose OAuth tokens, cloud credentials, MFA OTPs, `pass_enc_key`
    (the KEK that decrypts saved server passwords), or any other
    sensitive material the application places in the session.

    Caveat (real, not theoretical): SECRET_KEY currently lives in
    `pgadmin4.db` in the same DATA_DIR. A leak that includes BOTH
    `sessions/` and `pgadmin4.db` recovers the derived Fernet key and
    can decrypt session bodies. Closing this gap requires moving
    SECRET_KEY out of DATA_DIR (e.g., into the OS keychain via
    `USE_OS_SECRET_STORAGE`); tracked as Layer 2 follow-up.

    HKDF with a fixed salt and info string is used so the derivation is
    deterministic across processes (multiple workers must produce the
    same key) and so a future format change can swap in a new
    salt/info without compromising existing files.
    """
    key_material = secret.encode() if isinstance(secret, str) else secret
    derived = HKDF(
        algorithm=hashes.SHA256(),
        length=32,
        salt=_SESSION_FERNET_SALT,
        info=_SESSION_FERNET_INFO,
    ).derive(key_material)
    return Fernet(base64.urlsafe_b64encode(derived))


def _open_session_file(path):