fix: add startup validation to ReceiptWitness config

Add Pydantic model_validator to ReceiptWitnessSettings that fails fast
if session_encryption_key is missing or a placeholder value. Conditional
validation for resend_api_key when notifications_enabled=true.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

api/src/cartsnitch_api/middleware/rate_limit.py

@@ -4,6 +4,7 @@ Uses in-memory sliding window as fallback, Redis/DragonflyDB when available.
 Per-IP limiting on public endpoints, per-token limiting on authenticated endpoints.
 """
 
+import hashlib
 import time
 from collections import defaultdict
 from threading import Lock
@@ -71,8 +72,8 @@ def _get_rate_limit_key(request: Request) -> tuple[str, _SlidingWindowCounter]:
     auth_header = request.headers.get("authorization", "")
     if auth_header.startswith("Bearer "):
         token = auth_header[7:]
-        # Use last 16 chars of token as key to avoid storing full tokens
-        return f"token:{token[-16:]}", _auth_limiter
+        token_hash = hashlib.sha256(token.encode()).hexdigest()
+        return f"token:{token_hash}", _auth_limiter
 
     # Fallback to IP for unauthenticated non-public endpoints
     return f"ip:{_get_client_ip(request)}", _public_limiter

api/tests/test_middleware/test_rate_limit.py

@@ -1,8 +1,10 @@
 """Tests for rate limiting middleware."""
 
+from unittest.mock import MagicMock
+
 import pytest
 
-from cartsnitch_api.middleware.rate_limit import _SlidingWindowCounter
+from cartsnitch_api.middleware.rate_limit import _SlidingWindowCounter, _get_rate_limit_key
 
 
 class TestSlidingWindowCounter:
@@ -53,3 +55,32 @@ async def test_health_skips_rate_limit(client):
     resp = await client.get("/health")
     assert resp.status_code == 200
     assert "x-ratelimit-limit" not in resp.headers
+
+
+class TestGetRateLimitKey:
+    def _make_request(self, auth_header: str = "") -> MagicMock:
+        req = MagicMock()
+        req.url.path = "/purchases"
+        req.headers = {"authorization": auth_header} if auth_header else {}
+        return req
+
+    def test_distinct_tokens_produce_distinct_keys(self):
+        req1 = self._make_request("Bearer token_alpha_12345")
+        req2 = self._make_request("Bearer token_beta_67890")
+        key1, _ = _get_rate_limit_key(req1)
+        key2, _ = _get_rate_limit_key(req2)
+        assert key1 != key2
+
+    def test_same_token_produces_same_key(self):
+        req1 = self._make_request("Bearer same_token_value_abc")
+        req2 = self._make_request("Bearer same_token_value_abc")
+        key1, _ = _get_rate_limit_key(req1)
+        key2, _ = _get_rate_limit_key(req2)
+        assert key1 == key2
+
+    def test_key_does_not_contain_raw_token_suffix(self):
+        raw_token = "my_secret_jwt_token_xyz"
+        req = self._make_request(f"Bearer {raw_token}")
+        key, _ = _get_rate_limit_key(req)
+        assert raw_token[-16:] not in key
+        assert raw_token not in key

receiptwitness/src/receiptwitness/config.py

@@ -1,8 +1,12 @@
 """Service-specific configuration for ReceiptWitness."""
 
+from pydantic import model_validator
 from pydantic_settings import BaseSettings
 
 
+_PLACEHOLDER_VALUES = {"change-me-in-production"}
+
+
 class ReceiptWitnessSettings(BaseSettings):
     model_config = {"env_prefix": "RW_"}
 
@@ -30,5 +34,34 @@ class ReceiptWitnessSettings(BaseSettings):
     # Mailgun inbound email webhook
     mailgun_webhook_signing_key: str = ""
 
+    @model_validator(mode="after")
+    def validate_required_vars(self):
+        errors = []
+        if not self.session_encryption_key or self.session_encryption_key in _PLACEHOLDER_VALUES:
+            errors.append(
+                "RW_SESSION_ENCRYPTION_KEY must be set to a secure value. "
+                'Generate one with: python -c "from cryptography.fernet import Fernet; print(Fernet.generate_key().decode())"'
+            )
+        if self.notifications_enabled and not self.resend_api_key:
+            errors.append(
+                "RW_RESEND_API_KEY must be set when RW_NOTIFICATIONS_ENABLED=true. "
+                "Get an API key from https://resend.com/api-keys"
+            )
+        if errors:
+            raise ValueError(
+                "ReceiptWitness startup failed — missing required config:\n"
+                + "\n".join(f"  - {e}" for e in errors)
+            )
+        return self
 
-settings = ReceiptWitnessSettings()
+
+class _LazySettings:
+    _instance: ReceiptWitnessSettings | None = None
+
+    def __getattr__(self, name: str):
+        if _LazySettings._instance is None:
+            _LazySettings._instance = ReceiptWitnessSettings()
+        return getattr(_LazySettings._instance, name)
+
+
+settings = _LazySettings()

receiptwitness/tests/conftest.py

@@ -1,12 +1,16 @@
 """Shared test fixtures."""
 
 import json
+import os
 from pathlib import Path
 
 import pytest
 
 FIXTURES_DIR = Path(__file__).parent / "fixtures"
 
+os.environ.setdefault("RW_SESSION_ENCRYPTION_KEY", "test-secret-key-for-unit-tests-only-32bytes!")
+os.environ.setdefault("RW_MAILGUN_WEBHOOK_SIGNING_KEY", "test-mailgun-signing-key")
+
 
 @pytest.fixture
 def meijer_receipt_data() -> dict:

receiptwitness/tests/test_config.py

@@ -0,0 +1,46 @@
+import pytest
+from receiptwitness.config import ReceiptWitnessSettings
+
+
+def test_valid_config():
+    s = ReceiptWitnessSettings(
+        session_encryption_key="7reF42nmTwbdN21PBoubGp7h_FU8qSimstmlaMLoRK8="
+    )
+    assert s.session_encryption_key
+
+
+def test_missing_session_encryption_key_raises():
+    with pytest.raises(ValueError, match="RW_SESSION_ENCRYPTION_KEY"):
+        ReceiptWitnessSettings(session_encryption_key="")
+
+
+def test_placeholder_session_encryption_key_raises():
+    with pytest.raises(ValueError, match="RW_SESSION_ENCRYPTION_KEY"):
+        ReceiptWitnessSettings(session_encryption_key="change-me-in-production")
+
+
+def test_notifications_enabled_without_resend_key_raises():
+    with pytest.raises(ValueError, match="RW_RESEND_API_KEY"):
+        ReceiptWitnessSettings(
+            session_encryption_key="7reF42nmTwbdN21PBoubGp7h_FU8qSimstmlaMLoRK8=",
+            notifications_enabled=True,
+            resend_api_key="",
+        )
+
+
+def test_notifications_disabled_without_resend_key_ok():
+    s = ReceiptWitnessSettings(
+        session_encryption_key="7reF42nmTwbdN21PBoubGp7h_FU8qSimstmlaMLoRK8=",
+        notifications_enabled=False,
+        resend_api_key="",
+    )
+    assert s.notifications_enabled is False
+
+
+def test_notifications_enabled_with_resend_key_ok():
+    s = ReceiptWitnessSettings(
+        session_encryption_key="7reF42nmTwbdN21PBoubGp7h_FU8qSimstmlaMLoRK8=",
+        notifications_enabled=True,
+        resend_api_key="re_test_1234567890",
+    )
+    assert s.resend_api_key == "re_test_1234567890"