Ability to use MSAL in the Desktop (#225272)

* Ability to use MSAL in the Desktop

* add comment about MSAL workaround

extensions/microsoft-authentication/src/common/cachePlugin.ts

@@ -0,0 +1,55 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { ICachePlugin, TokenCacheContext } from '@azure/msal-node';
+import { Disposable, EventEmitter, SecretStorage } from 'vscode';
+
+export class SecretStorageCachePlugin implements ICachePlugin {
+	private readonly _onDidChange: EventEmitter<void> = new EventEmitter<void>();
+	readonly onDidChange = this._onDidChange.event;
+
+	private _disposable: Disposable;
+
+	private _value: string | undefined;
+
+	constructor(
+		private readonly _secretStorage: SecretStorage,
+		private readonly _key: string
+	) {
+		this._disposable = Disposable.from(
+			this._onDidChange,
+			this._registerChangeHandler()
+		);
+	}
+
+	private _registerChangeHandler() {
+		return this._secretStorage.onDidChange(e => {
+			if (e.key === this._key) {
+				this._onDidChange.fire();
+			}
+		});
+	}
+
+	async beforeCacheAccess(tokenCacheContext: TokenCacheContext): Promise<void> {
+		const data = await this._secretStorage.get(this._key);
+		this._value = data;
+		if (data) {
+			tokenCacheContext.tokenCache.deserialize(data);
+		}
+	}
+
+	async afterCacheAccess(tokenCacheContext: TokenCacheContext): Promise<void> {
+		if (tokenCacheContext.cacheHasChanged) {
+			const value = tokenCacheContext.tokenCache.serialize();
+			if (value !== this._value) {
+				await this._secretStorage.store(this._key, value);
+			}
+		}
+	}
+
+	dispose() {
+		this._disposable.dispose();
+	}
+}