feat(bot,wizard): smart message filtering, encrypted standalone wizard, and file persistence

backend/app/utils/draft_token.py

@@ -0,0 +1,81 @@
+"""HMAC-SHA256 token verification for standalone draft review."""
+import base64
+import hashlib
+import hmac
+import json
+import time
+from typing import Any
+from uuid import UUID
+
+def _b64url_encode(data: bytes) -> str:
+    return base64.urlsafe_b64encode(data).rstrip(b"=").decode("ascii")
+
+
+def _b64url_decode(s: str) -> bytes:
+    padding = 4 - (len(s) % 4)
+    if padding != 4:
+        s += "=" * padding
+    return base64.urlsafe_b64decode(s.encode("ascii"))
+
+
+def _get_secret(secret: str | None = None) -> str:
+    if secret:
+        return secret
+    try:
+        from app.config import settings
+        return settings.DRAFT_TOKEN_SECRET
+    except Exception:
+        return "procurement-draft-secret-change-in-prod-v7"
+
+
+def create_draft_token(
+    draft_id: str | UUID,
+    chat_id: int | None = None,
+    user_id: str | None = None,
+    secret: str | None = None,
+    expires_in: int = 7200,
+) -> str:
+    sec = _get_secret(secret)
+    now = int(time.time())
+    payload = {
+        "draft_id": str(draft_id),
+        "chat_id": chat_id,
+        "user_id": str(user_id) if user_id else None,
+        "iat": now,
+        "exp": now + expires_in,
+    }
+    payload_bytes = json.dumps(payload, separators=(",", ":"), ensure_ascii=False).encode("utf-8")
+    payload_b64 = _b64url_encode(payload_bytes)
+
+    sig = hmac.new(sec.encode("utf-8"), payload_b64.encode("ascii"), hashlib.sha256).digest()
+    sig_b64 = _b64url_encode(sig)
+
+    return f"{payload_b64}.{sig_b64}"
+
+
+def verify_draft_token(
+    token: str,
+    secret: str | None = None,
+) -> dict[str, Any] | None:
+    """Verify signature and expiration of a draft token. Return payload or None."""
+    if not token or "." not in token:
+        return None
+    try:
+        sec = _get_secret(secret)
+        payload_b64, sig_b64 = token.split(".", 1)
+        expected_sig = hmac.new(sec.encode("utf-8"), payload_b64.encode("ascii"), hashlib.sha256).digest()
+        actual_sig = _b64url_decode(sig_b64)
+
+        if not hmac.compare_digest(expected_sig, actual_sig):
+            return None
+
+        payload_bytes = _b64url_decode(payload_b64)
+        payload = json.loads(payload_bytes.decode("utf-8"))
+
+        exp = payload.get("exp")
+        if exp is not None and int(exp) < int(time.time()):
+            return None
+
+        return payload
+    except Exception:
+        return None