Add environment-driven CORS settings and backend regression tests

backend/.env.example

@@ -20,3 +20,7 @@ BANGUI_TIMEZONE=UTC
 
 # Application log level: debug | info | warning | error | critical
 BANGUI_LOG_LEVEL=info
+
+# Comma-separated list of allowed CORS origins when the frontend is served
+# from a different origin than the backend.
+BANGUI_CORS_ALLOWED_ORIGINS=http://localhost:5173

backend/app/config.py

@@ -41,6 +41,14 @@ class Settings(BaseSettings):
         default="UTC",
         description="IANA timezone name used when displaying timestamps in the UI.",
     )
+    cors_allowed_origins: list[str] = Field(
+        default_factory=lambda: ["http://localhost:5173"],
+        description=(
+            "Comma-separated list of allowed CORS origins when the frontend is "
+            "served from a different origin than the backend. "
+            "Leave empty to disable cross-origin requests in production."
+        ),
+    )
     log_level: str = Field(
         default="info",
         description="Application log level: debug | info | warning | error | critical.",

backend/app/main.py

@@ -345,15 +345,17 @@ def create_app(settings: Settings | None = None) -> FastAPI:
     set_setup_complete_cache(app, False)
 
     # --- CORS ---
-    # In production the frontend is served by the same origin.
-    # CORS is intentionally permissive only in development.
-    app.add_middleware(
-        CORSMiddleware,
-        allow_origins=["http://localhost:5173"],  # Vite dev server
-        allow_credentials=True,
-        allow_methods=["*"],
-        allow_headers=["*"],
-    )
+    # Allow origins configured by the runtime environment. In production,
+    # this should be explicitly set to the frontend origin(s) or left empty
+    # when the UI is served from the same origin as the API.
+    if resolved_settings.cors_allowed_origins:
+        app.add_middleware(
+            CORSMiddleware,
+            allow_origins=resolved_settings.cors_allowed_origins,
+            allow_credentials=True,
+            allow_methods=["*"],
+            allow_headers=["*"],
+        )
 
     # --- Middleware ---
     # Note: middleware is applied in reverse order of registration.

backend/tests/test_main.py

@@ -0,0 +1,50 @@
+"""Unit tests for backend application startup and middleware configuration."""
+
+from app.config import Settings
+from app.main import CORSMiddleware, create_app
+
+
+def test_create_app_configures_cors_from_settings() -> None:
+    """The FastAPI app registers CORS middleware with the configured origins."""
+    settings = Settings(
+        database_path="/tmp/test.db",
+        fail2ban_socket="/tmp/fake_fail2ban.sock",
+        fail2ban_config_dir="/tmp/fail2ban",
+        session_secret="test-secret-key-do-not-use-in-production",
+        session_duration_minutes=60,
+        timezone="UTC",
+        log_level="debug",
+        cors_allowed_origins=["https://frontend.example.com"],
+    )
+
+    app = create_app(settings=settings)
+    cors_middleware = [
+        middleware for middleware in app.user_middleware if middleware.cls is CORSMiddleware
+    ]
+
+    assert len(cors_middleware) == 1
+    assert cors_middleware[0].kwargs["allow_origins"] == ["https://frontend.example.com"]
+    assert cors_middleware[0].kwargs["allow_credentials"] is True
+    assert cors_middleware[0].kwargs["allow_methods"] == ["*"]
+    assert cors_middleware[0].kwargs["allow_headers"] == ["*"]
+
+
+def test_create_app_skips_cors_when_no_origins_are_configured() -> None:
+    """The FastAPI app does not add CORS middleware when no origins are configured."""
+    settings = Settings(
+        database_path="/tmp/test.db",
+        fail2ban_socket="/tmp/fake_fail2ban.sock",
+        fail2ban_config_dir="/tmp/fail2ban",
+        session_secret="test-secret-key-do-not-use-in-production",
+        session_duration_minutes=60,
+        timezone="UTC",
+        log_level="debug",
+        cors_allowed_origins=[],
+    )
+
+    app = create_app(settings=settings)
+    cors_middleware = [
+        middleware for middleware in app.user_middleware if middleware.cls is CORSMiddleware
+    ]
+
+    assert cors_middleware == []