az-auth: Add Azure Authentication plugin

Author: sniok

plugins/az-auth/.eslintignore

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+node_modules/
+dist/
+out/
+coverage/
+*.min.js
+*.bundle.js

plugins/az-auth/.gitignore

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+out
+dist
+node_modules
+vsix
+.vscode-test/
+*.vsix
+.DS_Store
+.eslintcache
+azure-api.js

plugins/az-auth/.npmrc

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+legacy-peer-deps=true

plugins/az-auth/README.md

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+## Azure Auth Headlamp plugin
+
+This plugin exposes functions to enable Azure Authentication.
+The plugin consists of two parts:
+
+1. `src-bin/azure-api.ts`
+
+A small CLI utility script that is bundled to `azure-api.js` and run by the Headlamp app in Node.js.
+It uses `@azure/identity` and its interactive browser credential to perform basic operations like logging in and out and requesting auth tokens.
+
+2. `src/index.tsx`
+
+A bridge that calls the utility and exposes an Azure SDK compatible credential. It adds a `window.azureAuth` property.