fix: use private npm feed in CI to bypass network isolation (#3564)

Add tools/Configure-PrivateNpmFeed.ps1 script that creates .npmrc files
pointing to the Azure Artifacts PowerShell_V2_Build npm feed. Update
install-tools.yml to run the script and authenticate via npmAuthenticate
before installing autorest and rush.

Two .npmrc files are configured at build time:
- Repo root: for global npm install commands (autorest, rush CLI)
- autorest.powershell/common/config/rush/.npmrc: for rush install

The Rush .npmrc in the repo retains the public registry default so
external contributors can still install from registry.npmjs.org.

Fixes #3563

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

Author: gavinbarron

.azure-pipelines/common-templates/install-tools.yml

@@ -29,7 +29,25 @@ steps:
     displayName: Install NodeJs
     inputs:
       versionSpec: 18.x
-      
+
+  - task: PowerShell@2
+    displayName: Configure private npm feed
+    inputs:
+      targetType: filePath
+      pwsh: true
+      filePath: $(Build.SourcesDirectory)/tools/Configure-PrivateNpmFeed.ps1
+      arguments: -SourcesDirectory "$(Build.SourcesDirectory)"
+
+  - task: npmAuthenticate@0
+    displayName: Authenticate to private npm feed
+    inputs:
+      workingFile: $(Build.SourcesDirectory)/.npmrc
+
+  - task: npmAuthenticate@0
+    displayName: Authenticate to private npm feed (Rush)
+    inputs:
+      workingFile: $(Build.SourcesDirectory)/autorest.powershell/common/config/rush/.npmrc
+
   - task: Npm@1
     displayName: Install AutoRest
     inputs:

tools/Configure-PrivateNpmFeed.ps1

@@ -0,0 +1,37 @@
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License.
+
+<#
+.SYNOPSIS
+    Configures .npmrc files to use a private Azure Artifacts npm feed.
+
+.DESCRIPTION
+    Creates .npmrc files at the repository root and in the Rush config directory
+    to redirect npm and Rush package installations to a private feed. This is
+    used in CI pipelines where network isolation rules block the public npm registry.
+
+.PARAMETER SourcesDirectory
+    The root directory of the repository. Defaults to the current directory.
+
+.PARAMETER Registry
+    The private npm registry URL.
+#>
+param(
+    [Parameter()]
+    [string]$SourcesDirectory = (Get-Location).Path,
+
+    [Parameter()]
+    [string]$Registry = "https://microsoftgraph.pkgs.visualstudio.com/0985d294-5762-4bc2-a565-161ef349ca3e/_packaging/PowerShell_V2_Build/npm/registry/"
+)
+
+$npmrcContent = "registry=$Registry`nalways-auth=true"
+
+# Create .npmrc at repo root for global npm installs (autorest, rush)
+$rootNpmrc = Join-Path $SourcesDirectory ".npmrc"
+Set-Content -Path $rootNpmrc -Value $npmrcContent -NoNewline
+Write-Host "Created $rootNpmrc"
+
+# Overwrite Rush .npmrc to use private feed for rush install
+$rushNpmrc = Join-Path $SourcesDirectory "autorest.powershell/common/config/rush/.npmrc"
+Set-Content -Path $rushNpmrc -Value $npmrcContent -NoNewline
+Write-Host "Updated $rushNpmrc"