Add persistent browser auth to connector canvas

Replace Azure CLI-only authentication with InteractiveBrowserCredential, protected sign-in lifecycle endpoints, and subscription refresh after sign-in. Persist the Azure Identity cache securely across extension reloads and align connector restart guidance with the GitHub Copilot app.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

extensions/connector-namespaces/README.md

@@ -6,14 +6,16 @@ session. Search by name or category, sign in to a connector, then restart the
 session to make its tools available to the agent.
 
 > The canvas talks to public Azure Resource Manager (`management.azure.com`)
-> using the signed-in Azure CLI account. The extension does not register its own
-> Entra application or persist Azure credentials.
+> using an interactive Microsoft Entra browser sign-in. It does not register its
+> own Entra application. Azure Identity persists the account session in the
+> operating system's encrypted credential store.
 
 ## Prerequisites
 
 - **GitHub Copilot CLI** (the host that loads canvas extensions).
-- **Azure CLI**, signed in with `az login`. The extension asks Azure CLI for a
-  short-lived ARM access token and refreshes it through the same broker.
+- A browser for Microsoft Entra sign-in. The extension prompts when Azure
+  authentication is required and restores the encrypted Azure Identity session
+  after extension or Copilot CLI restarts.
 - **An Azure subscription with a Connector Namespace** — resource type
   `Microsoft.Web/connectorGateways` (API version `2026-05-01-preview`). This is
   a preview resource provider; you must have access to it for the catalog to
@@ -41,14 +43,15 @@ The destination **scope** is chosen at install time:
 ## Usage
 
 1. Open the **MCP Connectors** canvas from Copilot CLI.
-2. The canvas loads subscriptions from your signed-in Azure CLI account. Pick an
+2. If prompted, choose **Sign in** and complete Microsoft Entra authentication
+   in the browser. The canvas reloads your subscriptions automatically. Pick an
    Azure **subscription** and a **Connector Namespace**. The choice is saved for
    future sessions (change it any time via **Change namespace**).
 3. Browse or filter the connector catalog, then **Connect**. A browser tab
    opens for Microsoft sign-in; complete it and the canvas updates on its own.
 4. Connected connectors move into **My MCPs**. Use **Sandbox** on a tile to open
    that server directly in the namespace MCP playground.
-5. Restart the Copilot CLI session so the agent can load the connected tools.
+5. Restart the GitHub Copilot app so the agent can load the connected tools.
 
 The extension registers the native `connector_namespaces_open_playground` tool,
 so GitHub Copilot can open a named connector from **My MCPs** without installing
@@ -59,9 +62,11 @@ an additional Agent Skill.
 - `extension.mjs` — entry point; declares the canvas, `open_sandbox` action, and
   native `connector_namespaces_open_playground` tool.
 - `server.mjs` — a loopback HTTP server (bound to `127.0.0.1` only) that serves
-  the canvas UI and the JSON/OAuth endpoints the iframe calls.
-- `armClient.mjs` — thin ARM client (token brokered by Azure CLI, public ARM
-  base only, SSRF-guarded path segments).
+  the canvas UI and the JSON/authentication endpoints the iframe calls.
+- `auth.mjs` — `InteractiveBrowserCredential` broker for sign-in lifecycle,
+  cancellation, encrypted token-cache persistence, and ARM token refresh.
+- `armClient.mjs` — thin ARM client (public ARM base only, SSRF-guarded path
+  segments).
 - `catalog.mjs` — fetches and curates the connector list for a namespace.
 - `install.mjs` — the connect/install pipeline (managed-API connection, consent,
   rollback on cancel, and native HTTPS MCP config registration).
@@ -71,9 +76,11 @@ an additional Agent Skill.
 
 ## Privacy & security
 
-- ARM tokens come from `az account get-access-token`, stay in process memory,
-  and are never logged or written by the extension. Azure CLI owns sign-in and
-  credential storage.
+- ARM tokens come from `@azure/identity`'s `InteractiveBrowserCredential` and
+  are never logged. Azure Identity stores its refreshable account cache through
+  the operating system's encrypted credential store. A non-secret account
+  locator is saved with user-only permissions so a new process can select that
+  cache entry; the extension never writes raw tokens to its artifact files.
 - All servers bind to loopback (`127.0.0.1`) and are never exposed externally.
 - ARM requests go only to `https://management.azure.com/`; path segments are
   validated to prevent SSRF-style host smuggling.