StaticTokenCredential

sdk/core/Azure.Core/CHANGELOG.md

@@ -6,6 +6,8 @@
 
 ### Features Added
 
+- Added `TokenCredential.Create` static method, which returns an instance of `TokenCredential` that uses the supplied delgates to produce an `AccessToken`. This would most typically be used when an token has previously been obtained from some other source and that token needs to be returned by a `TokenCredential` instance.
+
 ### Breaking Changes
 
 ### Bugs Fixed

sdk/core/Azure.Core/api/Azure.Core.net461.cs

@@ -463,6 +463,9 @@ internal RetryOptions() { }
     public abstract partial class TokenCredential
     {
         protected TokenCredential() { }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, Azure.Core.AccessToken> getToken) { throw null; }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, Azure.Core.AccessToken> getToken, System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<Azure.Core.AccessToken>> getTokenAsync) { throw null; }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<Azure.Core.AccessToken>> getTokenAsync) { throw null; }
         public abstract Azure.Core.AccessToken GetToken(Azure.Core.TokenRequestContext requestContext, System.Threading.CancellationToken cancellationToken);
         public abstract System.Threading.Tasks.ValueTask<Azure.Core.AccessToken> GetTokenAsync(Azure.Core.TokenRequestContext requestContext, System.Threading.CancellationToken cancellationToken);
     }

sdk/core/Azure.Core/api/Azure.Core.net5.0.cs

@@ -463,6 +463,9 @@ internal RetryOptions() { }
     public abstract partial class TokenCredential
     {
         protected TokenCredential() { }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, Azure.Core.AccessToken> getToken) { throw null; }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, Azure.Core.AccessToken> getToken, System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<Azure.Core.AccessToken>> getTokenAsync) { throw null; }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<Azure.Core.AccessToken>> getTokenAsync) { throw null; }
         public abstract Azure.Core.AccessToken GetToken(Azure.Core.TokenRequestContext requestContext, System.Threading.CancellationToken cancellationToken);
         public abstract System.Threading.Tasks.ValueTask<Azure.Core.AccessToken> GetTokenAsync(Azure.Core.TokenRequestContext requestContext, System.Threading.CancellationToken cancellationToken);
     }

sdk/core/Azure.Core/api/Azure.Core.netcoreapp2.1.cs

@@ -463,6 +463,9 @@ internal RetryOptions() { }
     public abstract partial class TokenCredential
     {
         protected TokenCredential() { }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, Azure.Core.AccessToken> getToken) { throw null; }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, Azure.Core.AccessToken> getToken, System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<Azure.Core.AccessToken>> getTokenAsync) { throw null; }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<Azure.Core.AccessToken>> getTokenAsync) { throw null; }
         public abstract Azure.Core.AccessToken GetToken(Azure.Core.TokenRequestContext requestContext, System.Threading.CancellationToken cancellationToken);
         public abstract System.Threading.Tasks.ValueTask<Azure.Core.AccessToken> GetTokenAsync(Azure.Core.TokenRequestContext requestContext, System.Threading.CancellationToken cancellationToken);
     }

sdk/core/Azure.Core/api/Azure.Core.netstandard2.0.cs

@@ -463,6 +463,9 @@ internal RetryOptions() { }
     public abstract partial class TokenCredential
     {
         protected TokenCredential() { }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, Azure.Core.AccessToken> getToken) { throw null; }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, Azure.Core.AccessToken> getToken, System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<Azure.Core.AccessToken>> getTokenAsync) { throw null; }
+        public static Azure.Core.TokenCredential Create(System.Func<Azure.Core.TokenRequestContext, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<Azure.Core.AccessToken>> getTokenAsync) { throw null; }
         public abstract Azure.Core.AccessToken GetToken(Azure.Core.TokenRequestContext requestContext, System.Threading.CancellationToken cancellationToken);
         public abstract System.Threading.Tasks.ValueTask<Azure.Core.AccessToken> GetTokenAsync(Azure.Core.TokenRequestContext requestContext, System.Threading.CancellationToken cancellationToken);
     }

sdk/core/Azure.Core/src/TokenCredential.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Threading;
 using System.Threading.Tasks;
+using Azure.Core.Pipeline;
 
 namespace Azure.Core
 {
@@ -29,5 +30,86 @@ public abstract class TokenCredential
         /// <returns>A valid <see cref="AccessToken"/>.</returns>
         /// <remarks>Caching and management of the lifespan for the <see cref="AccessToken"/> is considered the responsibility of the caller: each call should request a fresh token being requested.</remarks>
         public abstract AccessToken GetToken(TokenRequestContext requestContext, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Creates a static <see cref="TokenCredential"/> that accepts delegates which will produce an <see cref="AccessToken"/>.
+        /// </summary>
+        /// <remarks>
+        /// Typically, the <see cref="TokenCredential"/> created by this method is for use when you have already obtained an <see cref="AccessToken"/>
+        /// from some other source and need a <see cref="TokenCredential"/> that will simply return that token. Because the static token can expire,
+        /// the delegates offer a mechanism to handle <see cref="AccessToken"/> renewal.
+        /// </remarks>
+        /// <param name="getToken">A delegate that returns an <see cref="AccessToken"/>.</param>
+        /// <param name="getTokenAsync">A delegate that returns a <see cref="ValueTask"/> of type <see cref="AccessToken"/>.</param>
+        /// <returns></returns>
+        public static TokenCredential Create(
+            Func<TokenRequestContext, CancellationToken, AccessToken> getToken,
+            Func<TokenRequestContext, CancellationToken, ValueTask<AccessToken>> getTokenAsync) => new StaticTokenCredential(getToken, getTokenAsync);
+
+        /// <summary>
+        /// Creates a static <see cref="TokenCredential"/> that accepts delegates which will produce an <see cref="AccessToken"/>.
+        /// </summary>
+        /// <remarks>
+        /// Typically, the <see cref="TokenCredential"/> created by this method is for use when you have already obtained an <see cref="AccessToken"/>
+        /// from some other source and need a <see cref="TokenCredential"/> that will simply return that token. Because the static token can expire,
+        /// the delegates offer a mechanism to handle <see cref="AccessToken"/> renewal.
+        /// </remarks>
+        /// <param name="getToken">A delegate that returns an <see cref="AccessToken"/>.</param>
+        /// <returns></returns>
+        public static TokenCredential Create(
+            Func<TokenRequestContext, CancellationToken, AccessToken> getToken) => new StaticTokenCredential(getToken);
+
+        /// <summary>
+        /// Creates a static <see cref="TokenCredential"/> that accepts delegates which will produce an <see cref="AccessToken"/>.
+        /// </summary>
+        /// <remarks>
+        /// Typically, the <see cref="TokenCredential"/> created by this method is for use when you have already obtained an <see cref="AccessToken"/>
+        /// from some other source and need a <see cref="TokenCredential"/> that will simply return that token. Because the static token can expire,
+        /// the delegates offer a mechanism to handle <see cref="AccessToken"/> renewal.
+        /// </remarks>
+        /// <param name="getTokenAsync">A delegate that returns a <see cref="ValueTask"/> of type <see cref="AccessToken"/>.
+        /// If <see cref="GetToken"/> is called, the provided delegate will be executed sync over async.</param>
+        /// <returns></returns>
+        public static TokenCredential Create(
+            Func<TokenRequestContext, CancellationToken, ValueTask<AccessToken>> getTokenAsync) => new StaticTokenCredential(getTokenAsync);
+
+        private class StaticTokenCredential : TokenCredential
+        {
+            private readonly Func<TokenRequestContext, CancellationToken, AccessToken> _getToken;
+            private readonly Func<TokenRequestContext, CancellationToken, ValueTask<AccessToken>> _getTokenAsync;
+
+            internal StaticTokenCredential(
+                Func<TokenRequestContext, CancellationToken, AccessToken> getToken,
+                Func<TokenRequestContext, CancellationToken, ValueTask<AccessToken>> getTokenAsync)
+            {
+                _getToken = getToken;
+                _getTokenAsync = getTokenAsync;
+            }
+
+            internal StaticTokenCredential(
+                Func<TokenRequestContext, CancellationToken, AccessToken> getToken)
+            {
+                _getToken = getToken;
+                _getTokenAsync = (context, token) => new ValueTask<AccessToken>(_getToken(context, token));
+            }
+
+            internal StaticTokenCredential(
+                Func<TokenRequestContext, CancellationToken, ValueTask<AccessToken>> getTokenAsync)
+            {
+                _getToken = (context, token) => getTokenAsync(context, token)
+#pragma warning disable AZC0102 // Do not use GetAwaiter().GetResult(). Use the TaskExtensions.EnsureCompleted() extension method instead.
+                        .GetAwaiter().GetResult();
+#pragma warning restore AZC0102 // Do not use GetAwaiter().GetResult(). Use the TaskExtensions.EnsureCompleted() extension method instead.
+                _getTokenAsync = getTokenAsync;
+            }
+
+            /// <inheritdoc cref="GetTokenAsync"/>
+            public override ValueTask<AccessToken> GetTokenAsync(TokenRequestContext requestContext, CancellationToken cancellationToken) =>
+                _getTokenAsync(requestContext, cancellationToken);
+
+            /// <inheritdoc cref="GetToken"/>
+            public override AccessToken GetToken(TokenRequestContext requestContext, CancellationToken cancellationToken) =>
+                _getToken(requestContext, cancellationToken);
+        }
     }
 }

sdk/core/Azure.Core/tests/StaticTokenCredentialTests.cs

@@ -0,0 +1,61 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using NUnit.Framework;
+
+namespace Azure.Core.Tests
+{
+    public class StaticTokenCredentialTests
+    {
+        private static string[] scopes = { "https://default.mock.auth.scope/.default" };
+        private static CancellationToken ctx = new CancellationTokenSource(TimeSpan.FromMinutes(5)).Token;
+        private static string expectedToken = "token";
+        private static DateTimeOffset expires = DateTimeOffset.UtcNow;
+        private static AccessToken staticToken;
+        private static Func<TokenRequestContext, CancellationToken, AccessToken> getToken;
+        private static Func<TokenRequestContext, CancellationToken, ValueTask<AccessToken>> getTokenAsync;
+
+        private static IEnumerable<object[]> Credentials()
+        {
+            staticToken = new AccessToken(expectedToken, expires);
+            getToken = (context, token) =>
+            {
+                Assert.AreEqual(scopes, context.Scopes);
+                Assert.AreEqual(ctx, token);
+                return staticToken;
+            };
+            getTokenAsync = async (context, token) =>
+            {
+                Assert.AreEqual(scopes, context.Scopes);
+                Assert.AreEqual(ctx, token);
+                await Task.Yield();
+                return staticToken;
+            };
+            yield return new object[] { TokenCredential.Create(getTokenAsync) };
+            yield return new object[] { TokenCredential.Create(getToken) };
+            yield return new object[] { TokenCredential.Create(getToken, getTokenAsync) };
+        }
+
+        [TestCaseSource(nameof(Credentials))]
+        public async Task CreateGetTokenAsyncCallsDelegate(TokenCredential credential)
+        {
+            AccessToken actualToken = await credential.GetTokenAsync(new TokenRequestContext(scopes), ctx);
+
+            Assert.AreEqual(expectedToken, actualToken.Token);
+            Assert.AreEqual(expires, actualToken.ExpiresOn);
+        }
+
+        [TestCaseSource(nameof(Credentials))]
+        public void CreateGetTokenCallsDelegate(TokenCredential credential)
+        {
+            AccessToken actualToken = credential.GetToken(new TokenRequestContext(scopes), ctx);
+
+            Assert.AreEqual(expectedToken, actualToken.Token);
+            Assert.AreEqual(expires, actualToken.ExpiresOn);
+        }
+    }
+}

sdk/identity/Azure.Identity/samples/DefiningCustomCredentialTypes.md

@@ -2,40 +2,14 @@
 The Azure.Identity library covers a broad range of Azure Active Directory authentication scenarios. However, it's possible the credential implementations in Azure.Identity might not meet the specific needs your application, or an application might want to avoid taking a dependency on the Azure.Identity library.
 
 ## Authenticating with a prefetched access token
-The Azure.Identity library does not contain a `TokenCredential` implementation which can be constructed directly with an `AccessToken`. This is intentionally omitted as a main line scenario as access tokens expire frequently and have constrained usage. However, there are some scenarios where authenticating a service client with a prefetched token is necessary.
 
-In this example `StaticTokenCredential` implements the `TokenCredential` abstraction. It takes a prefetched access token in its constructor as a `string` or `AccessToken`, and simply returns that from its implementation of `GetToken` and `GetTokenAsync`.
+For scenarios where you need to authenticate with a prefetched access token, the `TokenCredential.Create` static method is available.
 
-```C# Snippet:StaticTokenCredential
-public class StaticTokenCredential : TokenCredential
-{
-    private AccessToken _token;
+The following example shows an how an application already using some other mechanism for acquiring tokens (in this case the hypothetical method `AquireTokenForScope`) could use the `TokenCredential.Create` to authenticate a `BlobClient`.
 
-    public StaticTokenCredential(string token) : this(new AccessToken(token, DateTimeOffset.MinValue)) { }
-
-    public StaticTokenCredential(AccessToken token)
-    {
-        _token = token;
-    }
-
-    public override AccessToken GetToken(TokenRequestContext requestContext, CancellationToken cancellationToken)
-    {
-        return _token;
-    }
-
-    public override ValueTask<AccessToken> GetTokenAsync(TokenRequestContext requestContext, CancellationToken cancellationToken)
-    {
-        return new ValueTask<AccessToken>(_token);
-    }
-}
-```
-
-Once the application has defined this credential type instances of it can be used to authenticate Azure SDK clients. The following example shows an how an application already using some other mechanism for acquiring tokens (in this case the hypothetical method `AquireTokenForScope`) could use the `StaticTokenCredential` to authenticate a `BlobClient`.
-
-```C# Snippet:StaticTokenCredentialUsage
-string token = GetTokenForScope("https://storage.azure.com/.default");
-
-var credential = new StaticTokenCredential(token);
+```C# Snippet:TokenCredentialCreateUsage
+AccessToken token = GetTokenForScope("https://storage.azure.com/.default");
+var credential = TokenCredential.Create((_, _) => token);
 
 var client = new BlobClient(new Uri("https://aka.ms/bloburl"), credential);
 ```
@@ -120,4 +94,4 @@ The following example shows an how the `OnBehalfOfCredential` could be used to a
 var oboCredential = new OnBehalfOfCredential(clientId, clientSecret, userAccessToken);
 
 var client = new SecretClient(new Uri("https://myvault.vault.azure.net/"), oboCredential);
-```
+```

sdk/identity/Azure.Identity/tests/samples/CustomCredentialSnippets.cs

@@ -14,45 +14,22 @@ namespace Azure.Identity.Tests.samples
 {
     public class CustomCredentialSnippets
     {
-        #region Snippet:StaticTokenCredential
-        public class StaticTokenCredential : TokenCredential
-        {
-            private AccessToken _token;
-
-            public StaticTokenCredential(string token) : this(new AccessToken(token, DateTimeOffset.MinValue)) { }
-
-            public StaticTokenCredential(AccessToken token)
-            {
-                _token = token;
-            }
-
-            public override AccessToken GetToken(TokenRequestContext requestContext, CancellationToken cancellationToken)
-            {
-                return _token;
-            }
-
-            public override ValueTask<AccessToken> GetTokenAsync(TokenRequestContext requestContext, CancellationToken cancellationToken)
-            {
-                return new ValueTask<AccessToken>(_token);
-            }
-        }
-        #endregion
-
         [Test]
-        public void StaticTokenCredentialUsage()
+        public void TokenCredentialCreateUsage()
         {
-            #region Snippet:StaticTokenCredentialUsage
-            string token = GetTokenForScope("https://storage.azure.com/.default");
-
-            var credential = new StaticTokenCredential(token);
+            #region Snippet:TokenCredentialCreateUsage
+            AccessToken token = GetTokenForScope("https://storage.azure.com/.default");
+#if SNIPPET
+            var credential = TokenCredential.Create((_, _) => token);
 
             var client = new BlobClient(new Uri("https://aka.ms/bloburl"), credential);
+#endif
             #endregion
         }
 
-        private string GetTokenForScope(string scope)
+        private AccessToken GetTokenForScope(string scope)
         {
-            return null;
+            return new AccessToken();
         }
 
         #region Snippet:ConfidentialClientCredential

sdk/identity/Azure.Identity/tests/samples/TokenCacheSnippets.cs

@@ -12,8 +12,6 @@ namespace Azure.Identity.Samples
 {
     public class TokenCacheSnippets
     {
-        private const string TOKEN_CACHE_PATH = "./tokencache.bin";
-
         public void Identity_TokenCache_PersistentDefault()
         {
             #region Snippet:Identity_TokenCache_PersistentDefault