Add Simple Account Picker for use with Always Encrypted (#9707)

Adds the ability for the user to select from two or more linked azure accounts, using an integrated UI dialog, when executing a query that requires a Always Encrypted column master key located in Azure Key Vault.

extensions/mssql/src/util/dataCache.ts

@@ -0,0 +1,37 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+export class DataItemCache<T> {
+
+	millisecondsToLive: number;
+	getValueFunction: (...args: any[]) => Promise<T>;
+	cachedItem: T;
+	fetchDate: Date;
+
+	constructor(getValueFunction: (...args: any[]) => Promise<T>, secondsToLive: number) {
+		this.millisecondsToLive = secondsToLive * 1000;
+		this.getValueFunction = getValueFunction;
+		this.cachedItem = undefined;
+		this.fetchDate = new Date(0);
+	}
+
+	public isCacheExpired(): boolean {
+		return (this.fetchDate.getTime() + this.millisecondsToLive) < new Date().getTime();
+	}
+
+	public async getData(...args: any[]): Promise<T> {
+		if (!this.cachedItem || this.isCacheExpired()) {
+			let data = await this.getValueFunction(...args);
+			this.cachedItem = data;
+			this.fetchDate = new Date();
+			return data;
+		}
+		return this.cachedItem;
+	}
+
+	public resetCache(): void {
+		this.fetchDate = new Date(0);
+	}
+}