Notify users when resetting password for an unregistered account (#1251)

[IshanA2007]

Closes #1251

⚠️ Draft for maintainer discussion — security tradeoff

Explicitly telling a user "no account exists" partially defeats Cognito's prevent_user_existence_errors = "ENABLED" (iac/cognito.tf:66) anti-enumeration protection — it lets an attacker probe which emails have accounts. The issue explicitly requests this behavior, and a prior attempt (PR #1254) was closed over exactly this tension. Opening as draft so maintainers can decide whether the UX win is worth the enumeration exposure.

Problem

Auth is fully Cognito-hosted. When someone requests a password reset (or email OTP) for an email with no account, Cognito silently no-ops — no email, no message — leaving the user confused.

Fix

New custom /forgot-password/ Django flow:

1. User enters email; the view looks it up in the local auth-user table case-insensitively (email__iexact).
2. No match → "No account is associated with that email address. Sign in with your UVA email to create an account."
3. Match → calls Cognito forgot_password via boto3 (computes SECRET_HASH when the app client has a secret) to send the reset email; redirects to login with a generic confirmation.
4. UserNotFoundException → same no-account message; other Cognito errors → generic retry (no existence leak) + logged.

Adds a "Forgot your password?" link to the login modal.

Leakage limiting: the success copy is deliberately generic ("If an account exists…") and Cognito-side errors never reveal existence — the only disclosure is the local-DB pre-check the issue asks for.

Verification (actually run — throwaway Postgres)

• manage.py check — no issues.
• New tcf_website/tests/test_auth.py — 8/8 pass (GET render, empty/unknown/known email, case-insensitivity, secret-hash on/off, UserNotFoundException, generic error).
• Existing test_redirects (33 incl. auth) — pass. ruff check — clean.

Follow-up

Rate-limit /forgot-password/ (per-IP + per-email) — it's unauthenticated and triggers Cognito calls/emails.

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🤖 Implemented with Claude Code.

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Review details

⚙️ Run configuration

Configuration used: defaults

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Run ID: c81ecbf5-b193-4215-aef9-af8aa25af26a

📥 Commits

Reviewing files that changed from the base of the PR and between ed955fb and 7e51024.

📒 Files selected for processing (6)

• tcf_website/templates/site/auth/forgot_password.html
• tcf_website/templates/site/common/modals/_login.html
• tcf_website/tests/test_auth.py
• tcf_website/urls.py
• tcf_website/views/__init__.py
• tcf_website/views/auth/__init__.py

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 1251-notify-unregistered-password-reset

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