Add auth expiry interceptor and session-expired redirect

Docs/Backend-Development.md

@@ -110,6 +110,7 @@ backend/
 - Use **Depends()** for dependency injection (database sessions, services, auth).
 - Group endpoints into routers by feature domain (`routers/jails.py`, `routers/bans.py`, …).
 - Use appropriate HTTP status codes: `201` for creation, `204` for deletion with no body, `404` for not found, etc.
+- Protected endpoints should return `401 Unauthorized` or `403 Forbidden` when the session is invalid or expired; the frontend treats these responses as a session-expiry event and redirects the user to `/login`.
 - Use **HTTPException** or custom exception handlers — never return error dicts manually.
 - **GET endpoints are read-only — never call `db.commit()` or execute INSERT/UPDATE/DELETE inside a GET handler.** If a GET path produces side-effects (e.g., caching resolved data), that write belongs in a background task, a scheduled flush, or a separate POST endpoint. Users and HTTP caches assume GET is idempotent and non-mutating.
 

Docs/Tasks.md

@@ -111,7 +111,7 @@ Issues are grouped by category and ordered roughly by severity. Each entry descr
 
 ---
 
-### TASK-006 — No 401 interceptor: expired sessions show broken pages instead of redirecting
+### TASK-006 — No 401 interceptor: expired sessions show broken pages instead of redirecting (done)
 
 **Where found:** `frontend/src/api/client.ts`, `request` function. All non-2xx responses including 401 are thrown as a generic `ApiError`. Consumers render "Failed to load…" messages instead of redirecting.
 

frontend/src/api/__tests__/client.test.ts

@@ -0,0 +1,52 @@
+import { describe, expect, it, beforeEach, vi } from "vitest";
+import { ApiError, get, isAuthError, SESSION_EXPIRED_EVENT } from "../client";
+
+describe("api/client", () => {
+  beforeEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("dispatches session-expired for 401 responses", async () => {
+    const dispatchSpy = vi.spyOn(window, "dispatchEvent");
+
+    global.fetch = vi.fn().mockResolvedValue({
+      ok: false,
+      status: 401,
+      text: vi.fn().mockResolvedValue("Unauthorized"),
+    });
+
+    await expect(get("/test")).rejects.toBeInstanceOf(ApiError);
+    expect(dispatchSpy).toHaveBeenCalledTimes(1);
+    const call = dispatchSpy.mock.calls[0];
+    expect(call).toBeDefined();
+    const event = call?.[0] as Event;
+    expect(event.type).toBe(SESSION_EXPIRED_EVENT);
+  });
+
+  it("dispatches session-expired for 403 responses", async () => {
+    const dispatchSpy = vi.spyOn(window, "dispatchEvent");
+
+    global.fetch = vi.fn().mockResolvedValue({
+      ok: false,
+      status: 403,
+      text: vi.fn().mockResolvedValue("Forbidden"),
+    });
+
+    await expect(get("/test")).rejects.toBeInstanceOf(ApiError);
+    expect(dispatchSpy).toHaveBeenCalledTimes(1);
+    const call = dispatchSpy.mock.calls[0];
+    expect(call).toBeDefined();
+    const event = call?.[0] as Event;
+    expect(event.type).toBe(SESSION_EXPIRED_EVENT);
+  });
+
+  it("does not treat non-auth errors as auth errors", () => {
+    const error = new ApiError(500, "Server error");
+    expect(isAuthError(error)).toBe(false);
+  });
+
+  it("recognizes 401 and 403 ApiError as auth errors", () => {
+    expect(isAuthError(new ApiError(401, "Unauthorized"))).toBe(true);
+    expect(isAuthError(new ApiError(403, "Forbidden"))).toBe(true);
+  });
+});

frontend/src/api/client.ts

@@ -39,6 +39,18 @@ export class ApiError extends Error {
   }
 }
 
+/** Custom event name emitted when the backend signals an expired or invalid session. */
+export const SESSION_EXPIRED_EVENT = "bangui:session-expired";
+
+/**
+ * Returns `true` when the error represents an expired or unauthorized session.
+ *
+ * @param err - The error returned from the API client.
+ */
+export function isAuthError(err: unknown): err is ApiError {
+  return err instanceof ApiError && (err.status === 401 || err.status === 403);
+}
+
 // ---------------------------------------------------------------------------
 // Internal helpers
 // ---------------------------------------------------------------------------
@@ -63,6 +75,13 @@ async function request<T>(url: string, options: RequestInit = {}): Promise<T> {
 
   if (!response.ok) {
     const body: string = await response.text();
+
+    if (response.status === 401 || response.status === 403) {
+      if (typeof window !== "undefined") {
+        window.dispatchEvent(new Event(SESSION_EXPIRED_EVENT));
+      }
+    }
+
     throw new ApiError(response.status, body);
   }
 

frontend/src/providers/AuthProvider.tsx

@@ -10,10 +10,13 @@
 import {
   createContext,
   useCallback,
+  useEffect,
   useMemo,
   useState,
 } from "react";
+import { useNavigate } from "react-router-dom";
 import * as authApi from "../api/auth";
+import { SESSION_EXPIRED_EVENT } from "../api/client";
 
 // ---------------------------------------------------------------------------
 // Types
@@ -64,6 +67,21 @@ export function AuthProvider({
     token: sessionStorage.getItem(SESSION_KEY),
     expiresAt: sessionStorage.getItem(SESSION_EXPIRES_KEY),
   }));
+  const navigate = useNavigate();
+
+  const handleSessionExpired = useCallback((): void => {
+    sessionStorage.removeItem(SESSION_KEY);
+    sessionStorage.removeItem(SESSION_EXPIRES_KEY);
+    setAuth({ token: null, expiresAt: null });
+    navigate("/login", { replace: true });
+  }, [navigate]);
+
+  useEffect((): (() => void) => {
+    window.addEventListener(SESSION_EXPIRED_EVENT, handleSessionExpired);
+    return (): void => {
+      window.removeEventListener(SESSION_EXPIRED_EVENT, handleSessionExpired);
+    };
+  }, [handleSessionExpired]);
 
   const isAuthenticated = useMemo<boolean>(() => {
     if (!auth.token || !auth.expiresAt) return false;

frontend/src/providers/__tests__/AuthProvider.test.tsx

@@ -0,0 +1,44 @@
+import { describe, expect, it, vi, beforeEach } from "vitest";
+import { render, screen, waitFor } from "@testing-library/react";
+import { type ReactElement } from "react";
+import { MemoryRouter, Route, Routes, useLocation } from "react-router-dom";
+import { FluentProvider, webLightTheme } from "@fluentui/react-components";
+import { AuthProvider } from "../AuthProvider";
+import { SESSION_EXPIRED_EVENT } from "../../api/client";
+
+function CurrentLocation(): ReactElement {
+  const location = useLocation();
+  return <div data-testid="location">{location.pathname}</div>;
+}
+
+describe("AuthProvider", () => {
+  beforeEach(() => {
+    sessionStorage.clear();
+    vi.restoreAllMocks();
+  });
+
+  it("clears auth state and redirects to /login when session-expired fires", async () => {
+    sessionStorage.setItem("bangui_token", "token");
+    sessionStorage.setItem("bangui_expires_at", new Date(Date.now() + 10000).toISOString());
+
+    render(
+      <FluentProvider theme={webLightTheme}>
+        <MemoryRouter initialEntries={["/private"]}>
+          <AuthProvider>
+            <Routes>
+              <Route path="*" element={<CurrentLocation />} />
+            </Routes>
+          </AuthProvider>
+        </MemoryRouter>
+      </FluentProvider>,
+    );
+
+    window.dispatchEvent(new Event(SESSION_EXPIRED_EVENT));
+
+    await waitFor(() => {
+      expect(screen.getByTestId("location")).toHaveTextContent("/login");
+    });
+    expect(sessionStorage.getItem("bangui_token")).toBeNull();
+    expect(sessionStorage.getItem("bangui_expires_at")).toBeNull();
+  });
+});

frontend/src/utils/__tests__/fetchError.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it, vi } from "vitest";
+import { ApiError } from "../../api/client";
+import { handleFetchError } from "../fetchError";
+
+describe("utils/fetchError", () => {
+  it("ignores AbortError errors", () => {
+    const setError = vi.fn();
+    handleFetchError(new DOMException("Aborted", "AbortError"), setError, "fallback");
+    expect(setError).not.toHaveBeenCalled();
+  });
+
+  it("ignores auth errors", () => {
+    const setError = vi.fn();
+    handleFetchError(new ApiError(401, "Unauthorized"), setError, "fallback");
+    expect(setError).not.toHaveBeenCalled();
+  });
+
+  it("sets fallback for normal errors", () => {
+    const setError = vi.fn();
+    handleFetchError(new Error("Oops"), setError, "fallback");
+    expect(setError).toHaveBeenCalledWith("Oops");
+  });
+});

frontend/src/utils/fetchError.ts

@@ -1,3 +1,5 @@
+import { isAuthError } from "../api/client";
+
 /**
  * Normalize fetch error handling across hooks.
  */
@@ -10,5 +12,9 @@ export function handleFetchError(
     return;
   }
 
+  if (isAuthError(err)) {
+    return;
+  }
+
   setError(err instanceof Error ? err.message : fallback);
 }