Implement automatic token refresh on 401 errors

[Prajeeth-12]

API Client Interceptor: Added 401 handling in api.js to automatically refresh access tokens using stored refresh tokens, retry requests once, and logout on failure.
Auth Context: Created AuthContext.jsx for managing user state, login, logout, and token storage in localStorage.
App Integration: Updated App.jsx to wrap with AuthProvider for global auth state.
Login Implementation: Enhanced Login.jsx to use auth context, handle form submission, and display errors.
Code Quality: Fixed lint errors in LanguagePicker.jsx, NotFound.jsx, and AuthContext.jsx (removed unused imports, added ESLint disable for hooks).
This pull request introduces authentication support to the frontend by implementing a context-based authentication system, integrating API calls for login and token refresh, and updating the login page to use these new mechanisms. The changes also include some minor cleanups to language and translation code.

Authentication system integration:

• Added a new AuthContext in frontend/src/contexts/AuthContext.jsx to manage authentication state, provide login/logout methods, and handle token storage and user context. ([frontend/src/contexts/AuthContext.jsxR1-R55](https://github.com/oss-slu/TheHealthApp/pull/56/files#diff-3a8c5a8347827277ca8eb529ec90ffc5e52fc5ff5de9b5b0f840b6c29a22bb13R1-R55))
• Wrapped the main app router in frontend/src/App.jsx with the AuthProvider, making authentication context available throughout the app. ([[1]](https://github.com/oss-slu/TheHealthApp/pull/56/files#diff-a0eba768ed9d2a17091f82d46efb5e1c988f08185cc1e9989366995cdb4e3ba9R5), [[2]](https://github.com/oss-slu/TheHealthApp/pull/56/files#diff-a0eba768ed9d2a17091f82d46efb5e1c988f08185cc1e9989366995cdb4e3ba9R37), [[3]](https://github.com/oss-slu/TheHealthApp/pull/56/files#diff-a0eba768ed9d2a17091f82d46efb5e1c988f08185cc1e9989366995cdb4e3ba9R52))

API and token management:

• Created a centralized API utility in frontend/src/api.js that attaches access tokens to requests, automatically refreshes tokens on 401 errors, and retries requests as needed. ([frontend/src/api.jsR1-R64](https://github.com/oss-slu/TheHealthApp/pull/56/files#diff-a89738858630f071121be18ff14b0d8ef770e718126254d86d2a0f0ce52d8547R1-R64))

Login flow updates:

• Refactored the login page in frontend/src/pages/auth/Login.jsx to use the new authentication context, handle login errors, and redirect on success. Also updated form field names to match backend expectations. ([[1]](https://github.com/oss-slu/TheHealthApp/pull/56/files#diff-99dd4f896ea3a584c44ebc6e0318b5444f81398d558006b60254e40ab3b37003R5-R42), [[2]](https://github.com/oss-slu/TheHealthApp/pull/56/files#diff-99dd4f896ea3a584c44ebc6e0318b5444f81398d558006b60254e40ab3b37003R57))

Minor code cleanups:

• Removed unused i18n imports from frontend/src/components/LanguagePicker.jsx and frontend/src/pages/NotFound.jsx. ([[1]](https://github.com/oss-slu/TheHealthApp/pull/56/files#diff-bddeb81dc2560b92f0f8a3906fb4409ee392229e87da1460bb1f897565e0ae9fL2), [[2]](https://github.com/oss-slu/TheHealthApp/pull/56/files#diff-5b757aa9c4126171b33886faf59f31c285c320deefa3b0adaf22f9e9c4cc6febL3-L11))

[Munazzah-Rakhangi]

Changes Required – Auth flow not functional

Tested locally on PR #56. The login and signup requests are currently blocked due to CORS errors — the preflight (OPTIONS /api/v1/auth/login) consistently returns 400 Bad Request, so the actual POST request never reaches the backend.

Please:

• Verify that the FastAPI CORS middleware is configured before all routes and includes:

allow_origins=["http://localhost:5173", "http://127.0.0.1:5173"]
allow_methods=[""]
allow_headers=[""]
allow_credentials=True

• Ensure that preflight requests return 200 so the browser can send the login/signup requests.
• Once fixed, please re-test the full authentication flow (login, token refresh, logout).
• If it’s already working on your side, please show me a quick demo during our Tuesday weekly meeting so we can confirm and approve the PR.