AAE-37746 Add front-channel-logout component documentation

docs/core/components/front-channel-logout.component.md

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+---
+Title: Front Channel Logout component
+Added: v1.0.0
+Status: Active
+Last reviewed: 2025-10-24
+---
+
+# [Front Channel Logout component](../../../lib/core/src/lib/auth/oidc/front-channel-logout.component.ts "Defined in front-channel-logout.component.ts")
+
+Handles an OpenID Connect (OIDC) Front-Channel Logout request by validating issuer and session identifiers and triggering a local logout when they match.
+
+## Contents
+
+- [Basic usage](#basic-usage)
+- [Details](#details)
+  - [What is Front-Channel Logout?](#what-is-front-channel-logout)
+  - [How matching works](#how-matching-works)
+  - [Security considerations](#security-considerations)
+  - [Logout scenarios](#logout-scenarios)
+- [See also](#see-also)
+
+## Basic usage
+
+This component has no UI; it performs logic on init. Add a route that points to it so that your Identity Provider (IdP) can call your application during a front-channel logout.
+
+```ts
+import { Routes } from '@angular/router';
+import { FrontChannelLogoutComponent } from '@adf/core';
+
+export const routes: Routes = [
+  { path: 'oidc/front-channel-logout', component: FrontChannelLogoutComponent }
+];
+```
+
+When the IdP performs a front-channel logout it will iframe / redirect the user's browser to a URL like:
+
+```text
+/oidc/frontchannel_logout?iss=https://issuer.example.com&sid=abc123-session-id
+```
+
+On initialisation the component compares those query parameters with locally stored values provided by `AuthService` and calls `logout()` if both match.
+
+## Details
+
+### What is Front-Channel Logout?
+
+Front-Channel Logout is part of the OIDC specification. The Identity Provider notifies relying parties (your SPA) of a logout by issuing an HTTP(S) request (often via an iframe). The client application must validate the request and clear its own session.
+
+### How matching works
+
+Inside `ngOnInit` the component:
+
+1. Reads `iss` and `sid` from `ActivatedRoute.snapshot.queryParamMap`.
+2. Retrieves the stored issuer and session id via `AuthService.getStoredIssuer()` and `AuthService.getStoredSessionId()`.
+3. Compares both pairs. Logout is executed only if:
+   - storedIssuer === issuerParam AND
+   - storedSessionId === sessionIdParam (and none are falsy).
+
+```ts
+const storedIssuerMatches = storedIssuer && issuerParam && storedIssuer === issuerParam;
+const storedSessionMatches = storedSessionId && sessionIdParam && storedSessionId === sessionIdParam;
+if (storedIssuerMatches && storedSessionMatches) {
+  authService.logout();
+}
+```
+
+If either value is missing or does not match, nothing happens.
+
+### Security considerations
+
+- The component performs strict equality checks; no partial matching.
+- Both parameters must be present and match; a single match will not trigger logout.
+- Avoid exposing sensitive data in query parameters beyond issuer (`iss`) and session identifier (`sid`).
+
+### Logout scenarios
+
+These scenarios outline when a logout is triggered or suppressed. 
+
+Key scenarios:
+
+| Scenario | Stored Issuer | URL Issuer | Stored SID | URL SID | Outcome |
+|----------|---------------|-----------|------------|---------|---------|
+| Full match | A | A | 123 | 123 | logout called |
+| Issuer mismatch | A | B | 123 | 123 | no logout |
+| SID mismatch | A | A | 123 | 999 | no logout |
+| Both mismatch | A | B | 123 | 999 | no logout |
+| Missing issuer | null | A | 123 | 123 | no logout |
+| Missing SID | A | A | null | 123 | no logout |
+| Missing URL issuer | A | null | 123 | 123 | no logout |
+| Missing URL SID | A | A | 123 | null | no logout |
+
+### See also
+
+- [OIDC Session Management / Front-Channel Logout specification](https://openid.net/specs/openid-connect-frontchannel-1_0.html#ExampleFrontchannel)
+- [Login component](login.component.md)
+- [Login Dialog component](login-dialog.component.md)