[msal-v5] Add local-network-access iframe attribute for Chrome 142+ compatibility (#8132)

Chrome 142 enables Local Network Access Restrictions by default, causing
`ssoSilent()` to fail with `BrowserAuthError: monitor_window_timeout`
when the iframe cannot access authorization servers on local networks.

## Changes

- **lib/msal-browser/src/interaction_handler/SilentHandler.ts**: Added
`allow="local-network-access *"` attribute to iframe created in
`createHiddenIframe()`
- **lib/msal-browser/test/interaction_handler/SilentHandler.spec.ts**:
Added test verifying the allow attribute is set correctly
- **change/@azure-msal-browser-*.json**: Beachball changefile for patch
release with PR link
[#8132](#8132)
- **lib/msal-browser/docs/iframe-usage.md**: Added documentation in the
"Browser restrictions" section explaining Chrome 142+ Local Network
Access Restrictions and how MSAL addresses them

## Technical Details

```typescript
function createHiddenIframe(): HTMLIFrameElement {
    const authFrame = document.createElement("iframe");
    // ... existing attributes ...
    authFrame.setAttribute("allow", "local-network-access *");  // Added
    document.body.appendChild(authFrame);
    return authFrame;
}
```

This replicates PR #8128 changes to the msal-v5 branch. The test was
adapted to match msal-v5's function signature (4 parameters vs 5 in
dev).

## Documentation

Added to `iframe-usage.md`:
- Chrome 142+ enables Local Network Access Restrictions by default
- This affects `ssoSilent()` when the iframe needs to access
authorization servers on local networks
- MSAL includes the `allow="local-network-access *"` iframe attribute to
address this restriction
- Users may still need to consent to local network access in their
browser, but the authentication flow will no longer timeout

## References

- Upstream PR: #8128
- Chrome Feature: [Local Network
Access](https://chromestatus.com/feature/5152728072060928)
- Related Issue: #8100

> [!WARNING]
>
> 







*This pull request was created as a result of the following prompt from
Copilot chat.*
> Replicate the changes from PR #8128 (Add local-network-access iframe
attribute for Chrome 142+ compatibility) so that they target the msal-v5
branch instead of dev. Ensure that all changes, including any new tests,
documentation, or code modifications related to the local-network-access
iframe attribute for Chrome 142+ compatibility, are included as they are
in the merged PR #8128.

<!-- START COPILOT CODING AGENT SUFFIX -->



<details>

<summary>Original prompt</summary>

> Replicate the changes from PR #8128 (Add local-network-access iframe
attribute for Chrome 142+ compatibility) so that they target the msal-v5
branch instead of dev. Ensure that all changes, including any new tests,
documentation, or code modifications related to the local-network-access
iframe attribute for Chrome 142+ compatibility, are included as they are
in the merged PR #8128.


</details>

*This pull request was created as a result of the following prompt from
Copilot chat.*
> Replicate the changes from PR #8128 (Add local-network-access iframe
attribute for Chrome 142+ compatibility) so that they target the msal-v5
branch instead of dev. Ensure that all changes, including any new tests,
documentation, or code modifications related to the local-network-access
iframe attribute for Chrome 142+ compatibility, are included as they are
in the merged PR #8128.

<!-- START COPILOT CODING AGENT TIPS -->
---

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our [2 minute survey](https://gh.io/copilot-coding-agent-survey).

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: tnorling <5307810+tnorling@users.noreply.github.com>
Co-authored-by: Thomas Norling <thomas.norling@microsoft.com>

Author: Copilot

change/@azure-msal-browser-f58c5c6e-8433-4f07-9f71-6e58bab22ab2.json

@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "Add allow=\"local-network-access *\" attribute to iframe for Chrome 142 compatibility [#8132](https://github.com/AzureAD/microsoft-authentication-library-for-js/pull/8132)",
+  "packageName": "@azure/msal-browser",
+  "email": "198982749+Copilot@users.noreply.github.com",
+  "dependentChangeType": "patch"
+}

lib/msal-browser/src/interaction_handler/SilentHandler.ts

@@ -200,6 +200,7 @@ function createHiddenIframe(): HTMLIFrameElement {
         "sandbox",
         "allow-scripts allow-same-origin allow-forms"
     );
+    authFrame.setAttribute("allow", "local-network-access *");
     document.body.appendChild(authFrame);
 
     return authFrame;

lib/msal-browser/test/interaction_handler/SilentHandler.spec.ts

@@ -61,6 +61,18 @@ describe("SilentHandler.ts Unit Tests", () => {
             );
             expect(authFrame instanceof HTMLIFrameElement).toBe(true);
         });
+
+        it("Sets the allow attribute for local network access on iframe", async () => {
+            const authFrame = await SilentHandler.initiateCodeRequest(
+                testNavUrl,
+                performanceClient,
+                browserRequestLogger,
+                RANDOM_TEST_GUID
+            );
+            expect(authFrame.getAttribute("allow")).toBe(
+                "local-network-access *"
+            );
+        });
     });
 
     describe("monitorIframeForHash", () => {