Bring back connectionString for Azure App Configuration. (#106)

Author: StephenMolloy

README.md

@@ -210,20 +210,19 @@ and currently exposes the format of the file which, as mentioned above, should b
 ```xml
 <add name="AzureAppConfig"
     [mode|@prefix|@stripPrefix|tokenPattern|@escapeExpandedValues|@optional=false]
-    @endpoint="https://your-appconfig-store.azconfig.io"
+    (@endpoint="https://your-appconfig-store.azconfig.io" | @connectionString="Endpoint=https://your-appconfig-store.azconfig.io;Id=XXXXXXXXXX;Secret=XXXXXXXXXX")
     [@keyFilter="string"]
     [@labelFilter="label"]
     [@acceptDateTime="DateTimeOffset"]
     [@useAzureKeyVault="bool"]
     type="Microsoft.Configuration.ConfigurationBuilders.AzureAppConfigurationBuilder, Microsoft.Configuration.ConfigurationBuilders.AzureAppConfig" />
 ```
 [AppConfiguration](https://docs.microsoft.com/en-us/azure/azure-app-configuration/overview) is a new offering from Azure, currently in preview. If you
-wish to use this new service for managing your configuration, then use this AzureAppConfigurationBuilder. `endpoint` is
-required, but all other attributes are optional.
-Previous iterations of this config builder allowed for a `connectionString` to connect to the
-App Configuration service. This method is no longer allowed, and this config builder now exclusively uses [DefaultAzureCredential](https://docs.microsoft.com/en-us/dotnet/api/azure.identity.defaultazurecredential)
-from the Azure.Identity package to handle credentials for connecting to the service.
+wish to use this new service for managing your configuration, then use this AzureAppConfigurationBuilder. Either `endpoint` or `connectionString` are
+required, but all other attributes are optional. If both `endpoint` and `connectionString` are used, then preference is given to the connection string.
   * `endpoint` - This specifies the AppConfiguration store to connect to.
+  * `connectionString` - This specifies the AppConfiguration store to connect to, along with the Id and Secret necessary to access the service. Be careful
+	not to expose any secrets in your code, repos, or App Configuration stores if you use this method for connecting.
   * `keyFilter` - Use this to select a set of configuration values matching a certain key pattern.
   * `labelFilter` - Only retrieve configuration values that match a certain label.
   * `acceptDateTime` - Instead of versioning ala Azure Key Vault, AppConfiguration uses timestamps. Use this attribute to go back in time

src/AzureAppConfig/AzureAppConfigurationBuilder.cs

@@ -28,14 +28,15 @@ public class AzureAppConfigurationBuilder : KeyValueConfigBuilder
 
         #pragma warning disable CS1591 // No xml comments for tag literals.
         public const string endpointTag = "endpoint";
-        public const string connectionStringTag = "connectionString";   // obsolete
+        public const string connectionStringTag = "connectionString";
         public const string keyFilterTag = "keyFilter";
         public const string labelFilterTag = "labelFilter";
         public const string dateTimeFilterTag = "acceptDateTime";
         public const string useKeyVaultTag = "useAzureKeyVault";
         #pragma warning restore CS1591 // No xml comments for tag literals.
 
         private Uri _endpoint;
+        private string _connectionString;
         private string _keyFilter;
         private string _labelFilter;
         private DateTimeOffset _dateTimeFilter;
@@ -82,34 +83,46 @@ protected override void LazyInitialize(string name, NameValueCollection config)
             if (_useKeyVault)
                 _kvClientCache = new ConcurrentDictionary<Uri, SecretClient>(EqualityComparer<Uri>.Default);
 
-            // Config Store Endpoint
-            string uri = UpdateConfigSettingWithAppSettings(endpointTag);
-            if (!String.IsNullOrWhiteSpace(uri))
+
+            // Always allow 'connectionString' to override black magic. But we expect this to be null most of the time.
+            _connectionString = UpdateConfigSettingWithAppSettings(connectionStringTag);
+            if (String.IsNullOrWhiteSpace(_connectionString))
             {
+                _connectionString = null;
+
+                // Use Endpoint instead
+                string uri = UpdateConfigSettingWithAppSettings(endpointTag);
+                if (!String.IsNullOrWhiteSpace(uri))
+                {
+                    try
+                    {
+                        _endpoint = new Uri(uri);
+                        _client = new ConfigurationClient(_endpoint, new DefaultAzureCredential());
+                    }
+                    catch (Exception ex)
+                    {
+                        if (!Optional)
+                            throw new ArgumentException($"Exception encountered while creating connection to Azure App Configuration store.", ex);
+                    }
+                }
+                else
+                {
+                    throw new ArgumentException($"An endpoint URI or connection string must be provided for connecting to Azure App Configuration service via the '{endpointTag}' or '{connectionStringTag}' attribute.");
+                }
+            }
+            else
+            {
+                // If we get here, then we should try to connect with a connection string.
                 try
                 {
-                    _endpoint = new Uri(uri);
-                    _client = new ConfigurationClient(_endpoint, new DefaultAzureCredential());
+                    _client = new ConfigurationClient(_connectionString);
                 }
                 catch (Exception ex)
                 {
                     if (!Optional)
                         throw new ArgumentException($"Exception encountered while creating connection to Azure App Configuration store.", ex);
                 }
             }
-            else
-            {
-                throw new ArgumentException($"An endpoint URI must be provided for connecting to Azure App Configuration service via the '{endpointTag}' attribute.");
-            }
-
-            if (config[connectionStringTag] != null)
-            {
-                // A connection string was given. Connection strings are no longer supported. Azure.Identity is the preferred way to
-                // authenticate, and that library has various mechanisms other than a plain text connection string in config to obtain
-                // the necessary client credentials for connecting to Azure.
-                // Be noisy about this even if optional, as it is a fundamental misconfiguration going forward.
-                throw new ArgumentException("AzureAppConfigurationBuilder no longer supports connection strings.", connectionStringTag);
-            }
 
             // At this point we've got all our ducks in a row and are ready to go. And we know that
             // we will be used, because this is the 'lazy' initializer. But let's handle one oddball case

src/packages/ConfigurationBuilders.AzureAppConfiguration.nupkg/tools/Net471/Install.ps1

@@ -12,7 +12,8 @@ $keyVaultConfigBuilder = [BuilderDescription]@{
 	Version="$assemblyVersion$";
 	DefaultName="AzureAppConfig";
 	AllowedParameters=@( $keyValueCommonParameters +
-		[ParameterDescription]@{ Name="endpoint"; IsRequired=$true; DefaultValue="[Config_Store_Endpoint_Url]" },
+		[ParameterDescription]@{ Name="endpoint"; IsRequired=$false; DefaultValue="[Config_Store_Endpoint_Url]" },
+		[ParameterDescription]@{ Name="connectionString"; IsRequired=$false },
 		[ParameterDescription]@{ Name="keyFilter"; IsRequired=$false },
 		[ParameterDescription]@{ Name="labelFilter"; IsRequired=$false },
 		[ParameterDescription]@{ Name="acceptDateTime"; IsRequired=$false };