feat: add OAuth error handling page for HuggingFace login failures #384 (PR -3)

[NaitikVerma6776]

Feature (PR-3)

Adds a dedicated error page at /auth/error to handle HuggingFace OAuth login failures gracefully instead of showing a blank/broken screen.

Changes

• Created frontend/src/app/auth/error/page.tsx
• Handles 5 error types with clear messages:
  • csrf_mismatch — Security/CSRF attack detected
  • token_exchange_failed — Token exchange failed
  • userinfo_failed — Profile fetch failed
  • email_required — Email not provided by HF
  • oauth_not_configured — Server misconfiguration
• "Try Again" button → redirects to /login
• "Go Home" button → redirects to /

🔗 Related Issue

Part of #384 — PR 3 of 4
Extends work from #136 resolved via PR #206

##Screenshots

🗂️ Type of Change

• ✨ New feature
• 🎨 UI / styling change

🧪 How was this tested?

• Ran the frontend locally (npm run dev inside frontend/)
• Tested all error codes via URL params ✅
• http://localhost:3000/auth/error ✅
• http://localhost:3000/auth/error?error=csrf_mismatch ✅
• http://localhost:3000/auth/error?error=email_required ✅
• http://localhost:3000/auth/error?error=oauth_not_configured ✅
• "Try Again" navigates to /login ✅
• "Go Home" navigates to / ✅

✅ Self-Review Checklist

• My branch is based on dev, not main
• I have not added any secrets / API keys
• I have not modified main branch
• My code follows the existing style
• No unnecessary formatting changes

📋 PR Series Status (Issue #384)

PR	Description	Status
PR 1	Settings page with HF token management	✅ Submitted
PR 2	HF token status in Dashboard/Header	✅ Already implemented in PR #206
PR 3	OAuth error handling page	✅ This PR
PR 4	HuggingFaceTokenModal improvements	🔄 Upcoming

[NaitikVerma6776]

⚠️ CI Failure Analysis — Pre-existing Issue

The failing Playwright test exists on the dev branch independently of this PR.

Proof:
GitHub Actions run on dev branch (triggered by PR #432):
https://github.com/param20h/PDF-Assistant-RAG/actions/runs/27055704867/job/79859570701

Same test failing on dev:
✘ logs in with email and password

My change: Added frontend/src/app/auth/error/page.tsx
Failing test: Login redirect to /dashboard

These have zero connection. The test fails because
the backend is unavailable in CI environment —
this is a pre-existing issue on the dev branch.

My PR Results:

• 8/9 tests passing ✅
• TypeScript build passing ✅
• PR Size Check passing ✅
• 1 pre-existing backend-dependent test failing ❌
  (same failure exists on dev branch)

Next Steps:
I would like to fix this pre-existing Playwright test failure in a separate PR by making the login test resilient to backend unavailability in CI.
Please let me know if I should raise a new issue for this.

Requesting review and merge.

[param20h]

⚠️ CI Failure Analysis — Pre-existing Issue

The failing Playwright test exists on the dev branch independently of this PR.

Proof:

GitHub Actions run on dev branch (triggered by PR #432):

https://github.com/param20h/PDF-Assistant-RAG/actions/runs/27055704867/job/79859570701

Same test failing on dev:

✘ logs in with email and password

My change: Added frontend/src/app/auth/error/page.tsx

Failing test: Login redirect to /dashboard

These have zero connection. The test fails because

the backend is unavailable in CI environment —

this is a pre-existing issue on the dev branch.

My PR Results:

• 8/9 tests passing ✅

• TypeScript build passing ✅

• PR Size Check passing ✅

• 1 pre-existing backend-dependent test failing ❌

  (same failure exists on dev branch)

Next Steps:

I would like to fix this pre-existing Playwright test failure in a separate PR by making the login test resilient to backend unavailability in CI.

Please let me know if I should raise a new issue for this.

Requesting review and merge.

Ok go with it

[NaitikVerma6776]

@param20h , kindly could you merge this PR as this is also a part of next PR which is PR -4 and also so that I could work on next one .

[NaitikVerma6776]

Hi @param20h,

I have raised PR #499 which fixes the pre-existing Playwright CI failure that is showing on this PR.
Kindly merge that PR first — once merged, all CI checks on this PR will pass cleanly.

[NaitikVerma6776]

Hi @param20h
This PR also includes PR 4 of issue #384— HuggingFaceTokenModal improvements:

1. Token format validation (must start with hf_)
2. Token preview (masked: hf_xxxx****xxxx)
3. Remove token button

All 4 PRs for issue #384 are now covered in this branch.
Please merge the previous PR#495 which is PR-3 of this issue.
Thank you for this opportunity to work on this amazing issue. Looking forward for more such work.