fix: SecurityHeadersMiddleware の CSP を OpenAPI パスで除外する (#112)

src/nene2/middleware/security_headers.py

@@ -1,6 +1,8 @@
 """Security headers middleware.
 
 Adds defensive HTTP headers to every response.
+CSP is skipped for OpenAPI documentation paths (/docs, /redoc, /openapi.json)
+because Swagger UI loads assets from CDN which would be blocked by default-src 'self'.
 """
 
 from starlette.middleware.base import BaseHTTPMiddleware, RequestResponseEndpoint
@@ -15,12 +17,21 @@
     "Permissions-Policy": "geolocation=(), microphone=()",
 }
 
+_OPENAPI_PATHS: frozenset[str] = frozenset({"/docs", "/redoc", "/openapi.json"})
+
 
 class SecurityHeadersMiddleware(BaseHTTPMiddleware):
-    """Attach security headers to every HTTP response."""
+    """Attach security headers to every HTTP response.
+
+    Content-Security-Policy is omitted for OpenAPI documentation paths so that
+    Swagger UI and ReDoc (which load assets from CDN) continue to work in development.
+    """
 
     async def dispatch(self, request: Request, call_next: RequestResponseEndpoint) -> Response:
         response = await call_next(request)
+        is_openapi_path = request.url.path in _OPENAPI_PATHS
         for header, value in _HEADERS.items():
+            if is_openapi_path and header == "Content-Security-Policy":
+                continue
             response.headers[header] = value
         return response

tests/nene2/middleware/test_security_headers.py

@@ -29,6 +29,16 @@ def test_security_headers_present() -> None:
     assert "Permissions-Policy" in response.headers
 
 
+def test_csp_absent_on_openapi_paths() -> None:
+    client = TestClient(_make_app())
+    for path in ("/docs", "/redoc", "/openapi.json"):
+        response = client.get(path)
+        assert "Content-Security-Policy" not in response.headers, (
+            f"CSP should not be set for {path}"
+        )
+        assert response.headers["X-Content-Type-Options"] == "nosniff"
+
+
 def test_security_headers_on_error_response() -> None:
     app = FastAPI()
     app.add_middleware(SecurityHeadersMiddleware)