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/cors.py

@@ -11,6 +11,6 @@ def add_cors_middleware(app: FastAPI) -> None:
         CORSMiddleware,
         allow_origins=settings.cors_origins,
         allow_credentials=True,
-        allow_methods=["*"],
-        allow_headers=["*"],
+        allow_methods=["GET", "POST", "PUT", "DELETE", "PATCH", "OPTIONS"],
+        allow_headers=["Content-Type", "Authorization", "Accept", "Origin", "X-Requested-With"],
     )

nginx.conf

@@ -9,6 +9,12 @@ server {
     gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript image/svg+xml;
     gzip_min_length 256;
 
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+    add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data: https:; font-src 'self'; connect-src 'self' https://*.cartsnitch.com https://*.farh.net; frame-ancestors 'self'" always;
+
     # Health endpoint for K8s probes
     location /health {
         access_log off;

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"