fix: redirect TPA account_settings errors to Account MFE with duplica…

[Gi-ron]

PR Description

When a SAML (or any third-party auth) error occurs during the Linked Accounts flow in the Account MFE, for example, AuthAlreadyAssociated when a user tries to link an IdP identity that is already linked to a different platform account the error context was silently lost before reaching the user.

Root cause: ExceptionMiddleware.get_redirect_uri() returned /account/settings, which is registered as a stateless RedirectView that redirects directly to ACCOUNT_MICROFRONTEND_URL without forwarding Django messages or query parameters. As a result, the user was redirected to the Account MFE with no indication of what went wrong.

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Changes

common/djangoapps/third_party_auth/pipeline.py

• Changed AUTH_DISPATCH_URLS[AUTH_ENTRY_ACCOUNT_SETTINGS] from /account/settings to /auth/account_settings_error.
• This routes error redirects through the new intermediate view instead of the stateless RedirectView.

common/djangoapps/third_party_auth/views.py

• Added account_settings_error_view: an intermediate Django view that reads the Django message left by SocialAuthExceptionMiddleware, resolves the human-readable provider name via provider.Registry.get_enabled_by_backend_name(), and redirects to the Account MFE with ?duplicate_provider=<provider_name>.
• This approach works for all backend types: SAML, OAuth2, and LTI.

common/djangoapps/third_party_auth/urls.py

• Registered the new view at auth/account_settings_error.

openedx/core/djangoapps/user_api/legacy_urls.py

• Added query_string=True to the existing /account/settings RedirectView as a defensive improvement, so any future redirects to that URL preserve query parameters.

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How it works

Before:

AuthAlreadyAssociated
→ ExceptionMiddleware → /account/settings
→ RedirectView (stateless) → Account MFE (no error context)

After:

AuthAlreadyAssociated
→ ExceptionMiddleware → /auth/account_settings_error
→ account_settings_error_view reads Django messages
→ Account MFE /?duplicate_provider=SimpleSAML+Local

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Screenshots

The user sees a clear error message in the Linked Accounts section.

Testing

Setup

1. Configure a SAML IdP (e.g. SimpleSAMLphp) as a Third Party Auth provider in Django Admin.
2. Create two platform accounts: user_a@example.com and user_b@example.com.
3. Log in as user_a and complete the SAML login flow to link the IdP identity to user_a.
4. Log out.

Reproduce the error

5. Log in as user_b.
6. Navigate to Account MFE → Linked Accounts.
7. Click Sign in with [provider name] for the same SAML IdP.
8. Complete authentication on the IdP side using the same identity used in step 3.

Expected result (after fix)

• The user is redirected to the Account MFE at: https://<LMS_HOST>/account/?duplicate_provider=<Provider+Name>

• The Account MFE displays the error message: The [Provider Name] account you selected is already linked to another [Site Name] account.

Expected result (before fix)

• The user is silently redirected to the Account MFE homepage with no error message.

Additional notes

After the AuthAlreadyAssociated error occurs, user_b will not be able to link the provider
until one of the following conditions is met:

• Sign out from the IdP session: Since the IdP session remains active after the error,
  user_b must sign out from the IdP (e.g. SimpleSAMLphp) before attempting to link again.
  Otherwise the IdP will silently reuse the same identity that is already linked to user_a,
  causing the error to repeat.

• user_a unlinks their account: If user_a disconnects the provider from their Open edX
  account via Account MFE → Linked Accounts → Unlink, the IdP identity becomes available
  again and user_b will be able to link it successfully on the next attempt.

[openedx-webhooks]

Thanks for the pull request, @Gi-ron!

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[mphilbrick211]

Hi @Gi-ron! It looks like you're contributing on behalf of eduNEXT. In order to have your CLA check turn green, please have your manager reach out to oscm@axim.org to have you added to our existing entity agreement.