Support load configuration settings from Azure Front Door

package.json

@@ -67,7 +67,7 @@
     "playwright": "^1.55.0"
   },
   "dependencies": {
-    "@azure/app-configuration": "^1.9.0",
+    "@azure/app-configuration": "^1.9.2",
     "@azure/core-rest-pipeline": "^1.6.0",
     "@azure/identity": "^4.2.1",
     "@azure/keyvault-secrets": "^4.7.0",

src/afd/afdRequestPipelinePolicy.ts

@@ -0,0 +1,35 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+import { PipelinePolicy } from "@azure/core-rest-pipeline";
+
+/**
+ * The pipeline policy that remove the authorization header from the request to allow anonymous access to the Azure Front Door.
+ * @remarks
+ * The policy position should be perRetry, since it should be executed after the "Sign" phase: https://github.com/Azure/azure-sdk-for-js/blob/main/sdk/core/core-client/src/serviceClient.ts
+ */
+export class AnonymousRequestPipelinePolicy implements PipelinePolicy {
+    name: string = "AppConfigurationAnonymousRequestPolicy";
+
+    async sendRequest(request, next) {
+        if (request.headers.has("authorization")) {
+            request.headers.delete("authorization");
+        }
+        return next(request);
+    }
+}
+
+/**
+ * The pipeline policy that remove the "sync-token" header from the request.
+ * The policy position should be perRetry. It should be executed after the SyncTokenPolicy in @azure/app-configuration, which is executed after retry phase: https://github.com/Azure/azure-sdk-for-js/blob/main/sdk/appconfiguration/app-configuration/src/appConfigurationClient.ts#L198
+ */
+export class RemoveSyncTokenPipelinePolicy implements PipelinePolicy {
+    name: string = "AppConfigurationRemoveSyncTokenPolicy";
+
+    async sendRequest(request, next) {
+        if (request.headers.has("sync-token")) {
+            request.headers.delete("sync-token");
+        }
+        return next(request);
+    }
+}

src/afd/constants.ts

@@ -0,0 +1,4 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+export const X_MS_DATE_HEADER = "x-ms-date";

src/appConfigurationImpl.ts

@@ -14,9 +14,10 @@ import {
     GetSnapshotOptions,
     ListConfigurationSettingsForSnapshotOptions,
     GetSnapshotResponse,
-    KnownSnapshotComposition
+    KnownSnapshotComposition,
+    ListConfigurationSettingPage
 } from "@azure/app-configuration";
-import { isRestError } from "@azure/core-rest-pipeline";
+import { isRestError, RestError } from "@azure/core-rest-pipeline";
 import { AzureAppConfiguration, ConfigurationObjectConstructionOptions } from "./appConfiguration.js";
 import { AzureAppConfigurationOptions } from "./appConfigurationOptions.js";
 import { IKeyValueAdapter } from "./keyValueAdapter.js";
@@ -67,6 +68,7 @@ import { ConfigurationClientManager } from "./configurationClientManager.js";
 import { getFixedBackoffDuration, getExponentialBackoffDuration } from "./common/backoffUtils.js";
 import { InvalidOperationError, ArgumentError, isFailoverableError, isInputError } from "./common/errors.js";
 import { ErrorMessages } from "./common/errorMessages.js";
+import { X_MS_DATE_HEADER } from "./afd/constants.js";
 
 const MIN_DELAY_FOR_UNHANDLED_FAILURE = 5_000; // 5 seconds
 
@@ -128,12 +130,17 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
     // Load balancing
     #lastSuccessfulEndpoint: string = "";
 
+    // Azure Front Door
+    #isAfdUsed: boolean = false;
+
     constructor(
         clientManager: ConfigurationClientManager,
         options: AzureAppConfigurationOptions | undefined,
+        isAfdUsed: boolean
     ) {
         this.#options = options;
         this.#clientManager = clientManager;
+        this.#isAfdUsed = isAfdUsed;
 
         // enable request tracing if not opt-out
         this.#requestTracingEnabled = requestTracingEnabled();
@@ -221,7 +228,8 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
             isFailoverRequest: this.#isFailoverRequest,
             featureFlagTracing: this.#featureFlagTracing,
             fmVersion: this.#fmVersion,
-            aiConfigurationTracing: this.#aiConfigurationTracing
+            aiConfigurationTracing: this.#aiConfigurationTracing,
+            isAfdUsed: this.#isAfdUsed
         };
     }
 
@@ -490,7 +498,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
      *                          If false, loads key-value using the key-value selectors. Defaults to false.
      */
     async #loadConfigurationSettings(loadFeatureFlag: boolean = false): Promise<ConfigurationSetting[]> {
-        const selectors = loadFeatureFlag ? this.#ffSelectors : this.#kvSelectors;
+        const selectors: PagedSettingsWatcher[] = loadFeatureFlag ? this.#ffSelectors : this.#kvSelectors;
 
         // Use a Map to deduplicate configuration settings by key. When multiple selectors return settings with the same key,
         // the configuration setting loaded by the later selector in the iteration order will override the one from the earlier selector.
@@ -509,6 +517,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
                     tagsFilter: selector.tagFilters
                 };
                 const { items, pageWatchers } = await this.#listConfigurationSettings(listOptions);
+
                 selector.pageWatchers = pageWatchers;
                 settings = items;
             } else { // snapshot selector
@@ -675,7 +684,9 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
             return Promise.resolve(false);
         }
 
-        const needRefresh = await this.#checkConfigurationSettingsChange(this.#ffSelectors);
+        let needRefresh = false;
+        needRefresh = await this.#checkConfigurationSettingsChange(this.#ffSelectors);
+
         if (needRefresh) {
             await this.#loadFeatureFlags();
         }
@@ -718,21 +729,38 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
                 const listOptions: ListConfigurationSettingsOptions = {
                     keyFilter: selector.keyFilter,
                     labelFilter: selector.labelFilter,
-                    tagsFilter: selector.tagFilters,
-                    pageEtags: pageWatchers.map(w => w.etag ?? "")
+                    tagsFilter: selector.tagFilters
                 };
 
+                if (!this.#isAfdUsed) {
+                    // if AFD is not used, add page etags to the listOptions to send conditional request
+                    listOptions.pageEtags = pageWatchers.map(w => w.etag ?? "") ;
+                }
+
                 const pageIterator = listConfigurationSettingsWithTrace(
                     this.#requestTraceOptions,
                     client,
                     listOptions
                 ).byPage();
 
+                let i = 0;
                 for await (const page of pageIterator) {
-                    // when conditional request is sent, the response will be 304 if not changed
-                    if (page._response.status === 200) { // created or changed
+                    const serverResponseTime: Date = this.#getMsDateHeader(page);
+                    if (i >= pageWatchers.length) {
                         return true;
                     }
+
+                    const lastServerResponseTime = pageWatchers[i].lastServerResponseTime;
+                    let isUpToDate = true;
+                    if (lastServerResponseTime !== undefined) {
+                        isUpToDate = serverResponseTime > lastServerResponseTime;
+                    }
+                    if (isUpToDate &&
+                        page._response.status === 200 && // conditional request returns 304 if not changed
+                        page.etag !== pageWatchers[i].etag) {
+                        return true;
+                    }
+                    i++;
                 }
             }
             return false;
@@ -743,7 +771,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
     }
 
     /**
-     * Gets a configuration setting by key and label.If the setting is not found, return undefine instead of throwing an error.
+     * Gets a configuration setting by key and label. If the setting is not found, return undefined instead of throwing an error.
      */
     async #getConfigurationSetting(configurationSettingId: ConfigurationSettingId, getOptions?: GetConfigurationSettingOptions): Promise<GetConfigurationSettingResponse | undefined> {
         const funcToExecute = async (client) => {
@@ -779,7 +807,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
 
             const items: ConfigurationSetting[] = [];
             for await (const page of pageIterator) {
-                pageWatchers.push({ etag: page.etag });
+                pageWatchers.push({ etag: page.etag, lastServerResponseTime: this.#getMsDateHeader(page) });
                 items.push(...page.items);
             }
             return { items, pageWatchers };
@@ -1107,6 +1135,25 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
             return first15Bytes.toString("base64url");
         }
     }
+
+    /**
+     * Extracts the response timestamp (x-ms-date) from the response headers. If not found, returns the current time.
+     */
+    #getMsDateHeader(response: GetConfigurationSettingResponse | ListConfigurationSettingPage | RestError): Date {
+        let header: string | undefined;
+        if (isRestError(response)) {
+            header = response.response?.headers?.get(X_MS_DATE_HEADER);
+        } else {
+            header = response._response?.headers?.get(X_MS_DATE_HEADER);
+        }
+        if (header !== undefined) {
+            const date = new Date(header);
+            if (!isNaN(date.getTime())) {
+                return date;
+            }
+        }
+        return new Date();
+    }
 }
 
 function getValidSettingSelectors(selectors: SettingSelector[]): SettingSelector[] {

src/common/errorMessages.ts

@@ -20,6 +20,9 @@ export const enum ErrorMessages {
     INVALID_LABEL_FILTER = "The characters '*' and ',' are not supported in label filters.",
     INVALID_TAG_FILTER = "Tag filter must follow the format 'tagName=tagValue'",
     CONNECTION_STRING_OR_ENDPOINT_MISSED = "A connection string or an endpoint with credential must be specified to create a client.",
+    REPLICA_DISCOVERY_NOT_SUPPORTED = "Replica discovery is not supported when loading from Azure Front Door.",
+    LOAD_BALANCING_NOT_SUPPORTED = "Load balancing is not supported when loading from Azure Front Door.",
+    WATCHED_SETTINGS_NOT_SUPPORTED = "Specifying watched settings is not supported when loading from Azure Front Door. If refresh is enabled, all loaded configuration settings will be watched automatically."
 }
 
 export const enum KeyVaultReferenceErrorMessages {

src/index.ts

@@ -3,6 +3,6 @@
 
 export { AzureAppConfiguration } from "./appConfiguration.js";
 export { Disposable } from "./common/disposable.js";
-export { load } from "./load.js";
+export { load, loadFromAzureFrontDoor } from "./load.js";
 export { KeyFilter, LabelFilter } from "./types.js";
 export { VERSION } from "./version.js";

src/load.ts

@@ -6,10 +6,18 @@ import { AzureAppConfiguration } from "./appConfiguration.js";
 import { AzureAppConfigurationImpl } from "./appConfigurationImpl.js";
 import { AzureAppConfigurationOptions } from "./appConfigurationOptions.js";
 import { ConfigurationClientManager } from "./configurationClientManager.js";
+import { AnonymousRequestPipelinePolicy, RemoveSyncTokenPipelinePolicy } from "./afd/afdRequestPipelinePolicy.js";
 import { instanceOfTokenCredential } from "./common/utils.js";
+import { ArgumentError } from "./common/errors.js";
+import { ErrorMessages } from "./common/errorMessages.js";
 
 const MIN_DELAY_FOR_UNHANDLED_ERROR_IN_MS: number = 5_000;
 
+// Empty token credential to be used when loading from Azure Front Door
+const emptyTokenCredential: TokenCredential = {
+    getToken: async () => ({ token: "", expiresOnTimestamp: Number.MAX_SAFE_INTEGER })
+};
+
 /**
  * Loads the data from Azure App Configuration service and returns an instance of AzureAppConfiguration.
  * @param connectionString  The connection string for the App Configuration store.
@@ -19,7 +27,7 @@ export async function load(connectionString: string, options?: AzureAppConfigura
 
 /**
  * Loads the data from Azure App Configuration service and returns an instance of AzureAppConfiguration.
- * @param endpoint  The URL to the App Configuration store.
+ * @param endpoint  The App Configuration store endpoint.
  * @param credential  The credential to use to connect to the App Configuration store.
  * @param options  Optional parameters.
  */
@@ -42,7 +50,8 @@ export async function load(
     }
 
     try {
-        const appConfiguration = new AzureAppConfigurationImpl(clientManager, options);
+        const isAfdUsed: boolean = credentialOrOptions === emptyTokenCredential;
+        const appConfiguration = new AzureAppConfigurationImpl(clientManager, options, isAfdUsed);
         await appConfiguration.load();
         return appConfiguration;
     } catch (error) {
@@ -56,3 +65,38 @@ export async function load(
         throw error;
     }
 }
+
+/**
+ * Loads the data from Azure Front Door and returns an instance of AzureAppConfiguration.
+ * @param endpoint  The Azure Front Door endpoint.
+ * @param appConfigOptions  Optional parameters.
+ */
+export async function loadFromAzureFrontDoor(endpoint: URL | string, options?: AzureAppConfigurationOptions): Promise<AzureAppConfiguration>;
+
+export async function loadFromAzureFrontDoor(
+    endpoint: string | URL,
+    appConfigOptions: AzureAppConfigurationOptions = {}
+): Promise<AzureAppConfiguration> {
+    if (appConfigOptions.replicaDiscoveryEnabled) {
+        throw new ArgumentError(ErrorMessages.REPLICA_DISCOVERY_NOT_SUPPORTED);
+    }
+    if (appConfigOptions.loadBalancingEnabled) {
+        throw new ArgumentError(ErrorMessages.LOAD_BALANCING_NOT_SUPPORTED);
+    }
+    if (appConfigOptions.refreshOptions?.watchedSettings && appConfigOptions.refreshOptions.watchedSettings.length > 0) {
+        throw new ArgumentError(ErrorMessages.WATCHED_SETTINGS_NOT_SUPPORTED);
+    }
+
+    appConfigOptions.replicaDiscoveryEnabled = false; // Disable replica discovery when loading from Azure Front Door
+
+    appConfigOptions.clientOptions = {
+        ...appConfigOptions.clientOptions,
+        additionalPolicies: [
+            ...(appConfigOptions.clientOptions?.additionalPolicies || []),
+            { policy: new AnonymousRequestPipelinePolicy(), position: "perRetry" },
+            { policy: new RemoveSyncTokenPipelinePolicy(), position: "perRetry" }
+        ]
+    };
+
+    return await load(endpoint, emptyTokenCredential, appConfigOptions);
+}

src/requestTracing/constants.ts

@@ -51,6 +51,7 @@ export const REPLICA_COUNT_KEY = "ReplicaCount";
 export const KEY_VAULT_CONFIGURED_TAG = "UsesKeyVault";
 export const KEY_VAULT_REFRESH_CONFIGURED_TAG = "RefreshesKeyVault";
 export const FAILOVER_REQUEST_TAG = "Failover";
+export const AFD_USED_TAG = "AFD";
 
 // Compact feature tags
 export const FEATURES_KEY = "Features";