Support Azure Front Door (#706)

* wip

* wip

* wip

* wip

* fix test

* wip

* wip

* wip

* add test

* update correlation context

* update

* only check response time for refresh trigger engine

* disallow sentinel key refresh for AFD

* add feature flag refresh test

* update

* resolve comments

* update

* update error message

* upgrade sdk version

* update test

Author: zhiyuanliang-ms

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/Afd/AfdConfigurationClientManager.cs

@@ -0,0 +1,57 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Azure.Data.AppConfiguration;
+using Microsoft.Extensions.Azure;
+using System;
+using System.Collections.Generic;
+
+namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Afd
+{
+    internal class AfdConfigurationClientManager : IConfigurationClientManager
+    {
+        private readonly ConfigurationClientWrapper _clientWrapper;
+
+        public AfdConfigurationClientManager(
+            IAzureClientFactory<ConfigurationClient> clientFactory,
+            Uri endpoint)
+        {
+            if (clientFactory == null)
+            {
+                throw new ArgumentNullException(nameof(clientFactory));
+            }
+
+            if (endpoint == null)
+            {
+                throw new ArgumentNullException(nameof(endpoint));
+            }
+
+            _clientWrapper = new ConfigurationClientWrapper(endpoint, clientFactory.CreateClient(endpoint.AbsoluteUri));
+        }
+
+        public IEnumerable<ConfigurationClient> GetClients()
+        {
+            return new List<ConfigurationClient> { _clientWrapper.Client };
+        }
+
+        public void RefreshClients()
+        {
+            return;
+        }
+
+        public bool UpdateSyncToken(Uri endpoint, string syncToken)
+        {
+            return false;
+        }
+
+        public Uri GetEndpointForClient(ConfigurationClient client)
+        {
+            if (client == null)
+            {
+                throw new ArgumentNullException(nameof(client));
+            }
+
+            return _clientWrapper.Client == client ? _clientWrapper.Endpoint : null;
+        }
+    }
+}

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/Afd/AfdPolicy.cs

@@ -0,0 +1,47 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Azure.Core;
+using Azure.Core.Pipeline;
+using System;
+
+namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Afd
+{
+    /// <summary>
+    /// HTTP pipeline policy that removes Authorization and Sync-Token headers from outgoing requests.
+    /// </summary>
+    internal class AfdPolicy : HttpPipelinePolicy
+    {
+        private const string AuthorizationHeader = "Authorization";
+        private const string SyncTokenHeader = "Sync-Token";
+
+        /// <summary>
+        /// Processes the HTTP message and removes Authorization and Sync-Token headers.
+        /// </summary>
+        /// <param name="message">The HTTP message.</param>
+        /// <param name="pipeline">The pipeline.</param>
+        public override void Process(HttpMessage message, ReadOnlyMemory<HttpPipelinePolicy> pipeline)
+        {
+            message.Request.Headers.Remove(AuthorizationHeader);
+
+            message.Request.Headers.Remove(SyncTokenHeader);
+
+            ProcessNext(message, pipeline);
+        }
+
+        /// <summary>
+        /// Processes the HTTP message and removes Authorization and Sync-Token headers.
+        /// </summary>
+        /// <param name="message">The HTTP message.</param>
+        /// <param name="pipeline">The pipeline.</param>
+        /// <returns>A task representing the asynchronous operation.</returns>
+        public override async System.Threading.Tasks.ValueTask ProcessAsync(HttpMessage message, ReadOnlyMemory<HttpPipelinePolicy> pipeline)
+        {
+            message.Request.Headers.Remove(AuthorizationHeader);
+
+            message.Request.Headers.Remove(SyncTokenHeader);
+
+            await ProcessNextAsync(message, pipeline).ConfigureAwait(false);
+        }
+    }
+}

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/Afd/EmptyTokenCredential.cs

@@ -0,0 +1,38 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Azure.Core;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Afd
+{
+    /// <summary>
+    /// A token credential that provides an empty token.
+    /// </summary>
+    internal class EmptyTokenCredential : TokenCredential
+    {
+        /// <summary>
+        /// Gets an empty token.
+        /// </summary>
+        /// <param name="requestContext">The context of the token request.</param>
+        /// <param name="cancellationToken">A cancellation token to cancel the operation.</param>
+        /// <returns>An empty access token.</returns>
+        public override AccessToken GetToken(TokenRequestContext requestContext, CancellationToken cancellationToken)
+        {
+            return new AccessToken(string.Empty, DateTimeOffset.MaxValue);
+        }
+
+        /// <summary>
+        /// Asynchronously gets an empty token.
+        /// </summary>
+        /// <param name="requestContext">The context of the token request.</param>
+        /// <param name="cancellationToken">A cancellation token to cancel the operation.</param>
+        /// <returns>A task that represents the asynchronous operation. The task result contains an empty access token.</returns>
+        public override ValueTask<AccessToken> GetTokenAsync(TokenRequestContext requestContext, CancellationToken cancellationToken)
+        {
+            return new ValueTask<AccessToken>(new AccessToken(string.Empty, DateTimeOffset.MaxValue));
+        }
+    }
+}

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationOptions.cs

@@ -4,6 +4,7 @@
 using Azure.Core;
 using Azure.Data.AppConfiguration;
 using Microsoft.Extensions.Azure;
+using Microsoft.Extensions.Configuration.AzureAppConfiguration.Afd;
 using Microsoft.Extensions.Configuration.AzureAppConfiguration.AzureKeyVault;
 using Microsoft.Extensions.Configuration.AzureAppConfiguration.Extensions;
 using Microsoft.Extensions.Configuration.AzureAppConfiguration.FeatureManagement;
@@ -132,7 +133,7 @@ internal IEnumerable<IKeyValueAdapter> Adapters
         /// <summary>
         /// Options used to configure the client used to communicate with Azure App Configuration.
         /// </summary>
-        internal ConfigurationClientOptions ClientOptions { get; } = GetDefaultClientOptions();
+        internal ConfigurationClientOptions ClientOptions { get; private set; } = GetDefaultClientOptions();
 
         /// <summary>
         /// Flag to indicate whether Key Vault options have been configured.
@@ -154,6 +155,11 @@ internal IEnumerable<IKeyValueAdapter> Adapters
         /// </summary>
         internal StartupOptions Startup { get; set; } = new StartupOptions();
 
+        /// <summary>
+        /// Gets a value indicating whether Azure Front Door is used.
+        /// </summary>
+        internal bool IsAfdUsed { get; private set; }
+
         /// <summary>
         /// Client factory that is responsible for creating instances of ConfigurationClient.
         /// </summary>
@@ -186,11 +192,12 @@ public AzureAppConfigurationOptions()
         public AzureAppConfigurationOptions SetClientFactory(IAzureClientFactory<ConfigurationClient> factory)
         {
             ClientFactory = factory ?? throw new ArgumentNullException(nameof(factory));
+
             return this;
         }
 
         /// <summary>
-        /// Specify what key-values to include in the configuration provider.
+        /// Specifies what key-values to include in the configuration provider.
         /// <see cref="Select"/> can be called multiple times to include multiple sets of key-values.
         /// </summary>
         /// <param name="keyFilter">
@@ -262,7 +269,7 @@ public AzureAppConfigurationOptions Select(string keyFilter, string labelFilter
         }
 
         /// <summary>
-        /// Specify a snapshot and include its contained key-values in the configuration provider.
+        /// Specifies a snapshot and include its contained key-values in the configuration provider.
         /// <see cref="SelectSnapshot"/> can be called multiple times to include key-values from multiple snapshots.
         /// </summary>
         /// <param name="name">The name of the snapshot in Azure App Configuration.</param>
@@ -351,7 +358,7 @@ public AzureAppConfigurationOptions Connect(string connectionString)
                 throw new ArgumentNullException(nameof(connectionString));
             }
 
-            return Connect(new List<string> { connectionString });
+            return Connect(new string[] { connectionString });
         }
 
         /// <summary>
@@ -362,6 +369,11 @@ public AzureAppConfigurationOptions Connect(string connectionString)
         /// </param>
         public AzureAppConfigurationOptions Connect(IEnumerable<string> connectionStrings)
         {
+            if (IsAfdUsed)
+            {
+                throw new InvalidOperationException(ErrorMessages.ConnectionConflict);
+            }
+
             if (connectionStrings == null || !connectionStrings.Any())
             {
                 throw new ArgumentNullException(nameof(connectionStrings));
@@ -395,7 +407,7 @@ public AzureAppConfigurationOptions Connect(Uri endpoint, TokenCredential creden
                 throw new ArgumentNullException(nameof(credential));
             }
 
-            return Connect(new List<Uri>() { endpoint }, credential);
+            return Connect(new Uri[] { endpoint }, credential);
         }
 
         /// <summary>
@@ -405,6 +417,11 @@ public AzureAppConfigurationOptions Connect(Uri endpoint, TokenCredential creden
         /// <param name="credential">Token credential to use to connect.</param>
         public AzureAppConfigurationOptions Connect(IEnumerable<Uri> endpoints, TokenCredential credential)
         {
+            if (IsAfdUsed)
+            {
+                throw new InvalidOperationException(ErrorMessages.ConnectionConflict);
+            }
+
             if (endpoints == null || !endpoints.Any())
             {
                 throw new ArgumentNullException(nameof(endpoints));
@@ -416,12 +433,40 @@ public AzureAppConfigurationOptions Connect(IEnumerable<Uri> endpoints, TokenCre
             }
 
             Credential = credential ?? throw new ArgumentNullException(nameof(credential));
-
             Endpoints = endpoints;
             ConnectionStrings = null;
             return this;
         }
 
+        /// <summary>
+        /// Connect the provider to Azure Front Door endpoint.
+        /// </summary>
+        /// <param name="endpoint">The endpoint of the Azure Front Door instance to connect to.</param>
+        public AzureAppConfigurationOptions ConnectAzureFrontDoor(Uri endpoint)
+        {
+            if ((Credential != null && !(Credential is EmptyTokenCredential)) || (ConnectionStrings?.Any() ?? false))
+            {
+                throw new InvalidOperationException(ErrorMessages.ConnectionConflict);
+            }
+
+            if (IsAfdUsed)
+            {
+                throw new InvalidOperationException(ErrorMessages.AfdConnectionConflict);
+            }
+
+            if (endpoint == null)
+            {
+                throw new ArgumentNullException(nameof(endpoint));
+            }
+
+            Credential ??= new EmptyTokenCredential();
+
+            Endpoints = new Uri[] { endpoint };
+            ConnectionStrings = null;
+            IsAfdUsed = true;
+            return this;
+        }
+
         /// <summary>
         /// Trims the provided prefix from the keys of all key-values retrieved from Azure App Configuration.
         /// </summary>