# SAML Single Sign-On

## Objective

Let organizations control app access through their own identity provider.

SAML SSO configured per organization, with attribute mapping, certificate rotation, and a break-glass login.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Configure SSO per organization, not globally. Two customers will have different providers, certificates, and attribute names.
2. Validate every assertion fully: signature against the configured certificate, issuer, audience, destination, and the not-before and not-on-or-after window. An assertion that fails any of these is rejected, not repaired.
3. Reject replayed assertions by recording assertion IDs for the length of their validity window.
4. Map identity provider attributes to app users by a stable identifier the provider guarantees, and only accept role or group claims that you have explicitly mapped in the app's own configuration.
5. Support two active signing certificates at once so a customer can rotate without a window of downtime.
6. Keep at least one break-glass administrator who can sign in without SSO, and audit every use of it. A misconfigured provider otherwise locks the whole organization out of the tool they need to fix it.
7. Do NOT trust anything in the assertion to grant privileges it was not mapped to — self-asserted admin claims are the classic SAML escalation.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- Clock skew between provider and app must be tolerated by a small fixed margin only, never by disabling time checks.
- An expired certificate must produce an actionable admin error and a warning ahead of expiry, not a generic login failure.
- Enforced SSO must decide what happens to existing password and OAuth logins for that domain: disable them, and say so before enforcement starts.
- Just-in-time provisioning must not create users outside the organization's verified domains.
- A user removed at the identity provider keeps their app session until it expires — revoke sessions on de-provisioning rather than relying on the next login.
- Identity-provider-initiated sign-in arrives with no local request to match; support it explicitly or reject it explicitly, and pick a safe landing destination.
- Encrypted assertions, signed responses, and signed assertions are different configurations — handle whichever the customer sends rather than assuming one.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] SSO is configured per organization with its own metadata and certificates.
- [ ] Signature, issuer, audience, destination, and time window are all verified on every assertion.
- [ ] Replayed assertions are rejected.
- [ ] Two signing certificates can be active at once, so rotation causes no outage.
- [ ] Only explicitly mapped claims affect roles or permissions.
- [ ] A break-glass administrator login exists and every use of it is audited.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.