done

app/services/signed_request.py

@@ -0,0 +1,107 @@
+"""
+Signed-request verification: EIP-191 signature that binds {action, wallet, timestamp, body}.
+
+Message format (human-readable — what the user sees in MetaMask):
+
+    TrumpSignal · {ACTION}
+    wallet: 0x...
+    timestamp: 1713724800000
+    body: <sha256_hex_of_canonical_json, or "-" for empty>
+
+Server verifies:
+  1. recovered signer == wallet
+  2. |now - timestamp| <= MAX_SKEW_SECONDS (5 min)
+  3. sha256(canonical_json(body)) matches the hash in the message
+  4. signature not seen before (replay cache, TTL = MAX_SKEW)
+
+Same scheme is used for writes (with body) and reads (body=None → "-").
+"""
+import hashlib
+import json
+import logging
+import time
+from typing import Any, Optional
+
+from eth_account import Account
+from eth_account.messages import encode_defunct
+from fastapi import HTTPException
+
+logger = logging.getLogger(__name__)
+
+MAX_SKEW_SECONDS = 300  # 5 minutes
+
+
+def canonical_body_hash(body: Optional[Any]) -> str:
+    """Stable sha256 of a Python dict/primitive. `None` → '-'."""
+    if body is None:
+        return "-"
+    payload = json.dumps(body, sort_keys=True, separators=(",", ":"), default=str)
+    return hashlib.sha256(payload.encode("utf-8")).hexdigest()
+
+
+def build_message(action: str, wallet: str, timestamp_ms: int, body_hash: str) -> str:
+    return (
+        f"TrumpSignal · {action}\n"
+        f"wallet: {wallet.lower()}\n"
+        f"timestamp: {timestamp_ms}\n"
+        f"body: {body_hash}"
+    )
+
+
+# ── Replay cache ──────────────────────────────────────────────────────────
+# In-memory; fine for a single-process deploy. For multi-worker, move to Redis.
+_seen: dict[str, float] = {}  # sha256(signature) → expiry epoch seconds
+
+
+def _cache_put(sig: str, ttl: float) -> bool:
+    """Return True if sig was new, False if replay."""
+    now = time.time()
+    # lazy purge
+    if len(_seen) > 5000:
+        for k, v in list(_seen.items()):
+            if v < now:
+                _seen.pop(k, None)
+    key = hashlib.sha256(sig.encode("utf-8")).hexdigest()
+    if key in _seen and _seen[key] > now:
+        return False
+    _seen[key] = now + ttl
+    return True
+
+
+# ── Public API ────────────────────────────────────────────────────────────
+def verify_signed_request(
+    *,
+    action: str,
+    wallet: str,
+    timestamp_ms: int,
+    signature: str,
+    body: Optional[Any],
+    allow_replay: bool = False,
+) -> None:
+    """Raise HTTPException(401/422) if invalid. Silent on success.
+
+    allow_replay=True skips the nonce cache — use only for idempotent reads
+    (e.g. GET /user). Timestamp expiry still bounds the window to MAX_SKEW.
+    """
+    wallet = wallet.lower().strip()
+
+    # 1. Freshness
+    now_ms = int(time.time() * 1000)
+    if abs(now_ms - timestamp_ms) > MAX_SKEW_SECONDS * 1000:
+        raise HTTPException(401, "Signed request expired or clock skew too large")
+
+    # 2. Recover signer
+    body_hash = canonical_body_hash(body)
+    message = build_message(action, wallet, timestamp_ms, body_hash)
+    try:
+        recovered = Account.recover_message(encode_defunct(text=message), signature=signature).lower()
+    except Exception as exc:
+        logger.warning("Signature recovery failed (%s): %s", action, exc)
+        raise HTTPException(401, "Signature verification failed")
+    if recovered != wallet:
+        raise HTTPException(401, "Signature does not match wallet")
+
+    # 3. Replay guard (writes only)
+    if not allow_replay:
+        if not _cache_put(signature, ttl=MAX_SKEW_SECONDS):
+            raise HTTPException(401, "Signature already used (replay blocked)")