Add DefaultAzureIdentity support (#155)

* Add DefaultAzureIdentity support for blob snapshot

* Add documentation.

README.md

@@ -21,6 +21,22 @@ akka.persistence.snapshot-store.azure-blob-store.connection-string = "Your Azure
 akka.persistence.snapshot-store.azure-blob-store.container-name = "Your container name"
 ```
 
+### Configuring snapshots Blob Storage using DefaultAzureCredential
+
+You can use `Azure.Identity` `DefaultAzureCredential` to configure the resource by using `AzureBlobSnapshotSetup`. When using `DefaultAzureCredential`, the HOCON 'connection-string' setting is ignored.
+
+Example:
+```
+var blobStorageSetup = AzureBlobSnapshotSetup.Create(
+  new Uri("https://{account_name}.blob.core.windows.net"), // This is the blob service URI
+  new DefaultAzureCredential() // You can pass a DefaultAzureCredentialOption here.
+                               // https://docs.microsoft.com/en-us/dotnet/api/azure.identity.defaultazurecredential?view=azure-dotnet
+);
+
+var bootstrap = BootstrapSetup.Create().And(blobStorageSetup);
+var system = ActorSystem.Create("actorSystem", bootstrap);
+```
+
 ## Using the plugin in local development environment
 
 You can use this plugin with Azure Storage Emulator in a local development environment by setting the development flag in the configuration file:

src/Akka.Persistence.Azure/Akka.Persistence.Azure.csproj

@@ -15,6 +15,7 @@
 
   <ItemGroup>
     <PackageReference Include="Akka.Persistence.Query" Version="$(AkkaVersion)" />
+    <PackageReference Include="Azure.Identity" Version="1.3.0" />
     <PackageReference Include="Azure.Storage.Blobs" Version="12.8.1" />
     <PackageReference Include="Microsoft.Azure.Cosmos.Table" Version="1.0.8" />
     <PackageReference Include="System.Linq.Async" Version="5.0.0" />

src/Akka.Persistence.Azure/Snapshot/AzureBlobSnapshotSetup.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Akka.Actor.Setup;
+using Azure.Identity;
+using Azure.Storage.Blobs;
+
+namespace Akka.Persistence.Azure.Snapshot
+{
+    public class AzureBlobSnapshotSetup : Setup
+    {
+        /// <summary>
+        /// Create a new <see cref="AzureBlobSnapshotSetup"/>
+        /// </summary>
+        /// <param name="serviceUri">
+        /// A <see cref="Uri"/> referencing the blob service.
+        /// This is likely to be similar to "https://{account_name}.blob.core.windows.net".
+        /// </param>
+        /// <param name="defaultAzureCredential">
+        /// The <see cref="DefaultAzureCredential"/> used to sign requests.
+        /// </param>
+        /// <param name="blobClientOptions">
+        /// Optional client options that define the transport pipeline policies for authentication,
+        /// retries, etc., that are applied to every request.
+        /// </param>
+        /// <returns>A new <see cref="AzureBlobSnapshotSetup"/> instance</returns>
+        public static AzureBlobSnapshotSetup Create(
+            Uri serviceUri, 
+            DefaultAzureCredential defaultAzureCredential,
+            BlobClientOptions blobClientOptions = default)
+            => new AzureBlobSnapshotSetup(serviceUri, defaultAzureCredential, blobClientOptions);
+
+        private AzureBlobSnapshotSetup(
+            Uri serviceUri, 
+            DefaultAzureCredential azureCredential,
+            BlobClientOptions blobClientOptions)
+        {
+            ServiceUri = serviceUri;
+            DefaultAzureCredential = azureCredential;
+            BlobClientOptions = blobClientOptions;
+        }
+
+        public Uri ServiceUri { get; }
+
+        public DefaultAzureCredential DefaultAzureCredential { get; }
+
+        public BlobClientOptions BlobClientOptions { get; }
+    }
+}

src/Akka.Persistence.Azure/Snapshot/AzureBlobSnapshotStore.cs

@@ -54,9 +54,25 @@ public AzureBlobSnapshotStore(Config config = null)
                 ? AzurePersistence.Get(Context.System).BlobSettings
                 : AzureBlobSnapshotStoreSettings.Create(config);
 
-            _serviceClient = _settings.Development ?
-                new BlobServiceClient("UseDevelopmentStorage=true") :
-                new BlobServiceClient(_settings.ConnectionString);
+            if (_settings.Development)
+            {
+                _serviceClient = new BlobServiceClient("UseDevelopmentStorage=true");
+            }
+            else
+            {
+                var credentialSetup = Context.System.Settings.Setup.Get<AzureBlobSnapshotSetup>();
+                if (credentialSetup.HasValue)
+                {
+                    _serviceClient = new BlobServiceClient(
+                        credentialSetup.Value.ServiceUri,
+                        credentialSetup.Value.DefaultAzureCredential,
+                        credentialSetup.Value.BlobClientOptions);
+                }
+                else
+                {
+                    _serviceClient = new BlobServiceClient(_settings.ConnectionString);
+                }
+            }
 
             _containerClient = new Lazy<BlobContainerClient>(() => InitCloudStorage(5).Result);
         }