Add a callback for background token refresh outcomes

src/client/Microsoft.Identity.Client/AppConfig/ApplicationConfiguration.cs

@@ -145,6 +145,16 @@ public string ClientVersion
         /// </summary>
         public Func<AssertionRequestOptions, ExecutionResult, Task> OnCompletion { get; set; }
 
+        /// <summary>
+        /// Callback invoked when a fire-and-forget background (proactive) token refresh completes, giving
+        /// callers visibility into an otherwise-unobservable path. Receives an <see cref="ExecutionResult"/>
+        /// describing the outcome: on success <see cref="ExecutionResult.Result"/> is the refreshed token; on
+        /// failure <see cref="ExecutionResult.Exception"/> is the thrown exception (whose
+        /// <see cref="MsalException.AuthenticationResultMetadata"/> carries the failed attempt's HTTP duration).
+        /// Only set for confidential-client and managed-identity applications.
+        /// </summary>
+        public Func<ExecutionResult, Task> OnBackgroundTokenRefreshCompleted { get; set; }
+
         #endregion
 
         #region ClientCredentials

src/client/Microsoft.Identity.Client/Extensibility/ConfidentialClientApplicationBuilderExtensions.cs

@@ -189,5 +189,38 @@ public static ConfidentialClientApplicationBuilder OnCompletion(
             builder.Config.OnCompletion = onCompletion;
             return builder;
         }
+
+        /// <summary>
+        /// Configures an async callback invoked when a fire-and-forget background (proactive) token refresh completes.
+        /// Proactive refresh runs on a background thread after the caller has already received a valid cached token,
+        /// so its outcome (latency, failures) is otherwise unobservable. This callback surfaces it, e.g. for telemetry.
+        /// </summary>
+        /// <param name="builder">The confidential client application builder.</param>
+        /// <param name="onBackgroundTokenRefreshCompleted">
+        /// An async callback that receives the <see cref="ExecutionResult"/> of the background refresh. On success,
+        /// <see cref="ExecutionResult.Result"/> holds the refreshed token; on failure, <see cref="ExecutionResult.Exception"/>
+        /// holds the exception, whose <see cref="MsalException.AuthenticationResultMetadata"/> carries the failed
+        /// attempt's HTTP duration.
+        /// </param>
+        /// <returns>The builder to chain additional configuration calls.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="onBackgroundTokenRefreshCompleted"/> is null.</exception>
+        /// <remarks>
+        /// <para>Invoked on a background thread. Check <see cref="ExecutionResult.Successful"/> to determine the outcome.</para>
+        /// <para>Exceptions thrown by this callback are caught and logged internally so they cannot disrupt the refresh.</para>
+        /// </remarks>
+        public static ConfidentialClientApplicationBuilder OnBackgroundTokenRefreshCompleted(
+            this ConfidentialClientApplicationBuilder builder,
+            Func<ExecutionResult, Task> onBackgroundTokenRefreshCompleted)
+        {
+            builder.ValidateUseOfExperimentalFeature();
+
+            if (onBackgroundTokenRefreshCompleted == null)
+            {
+                throw new ArgumentNullException(nameof(onBackgroundTokenRefreshCompleted));
+            }
+
+            builder.Config.OnBackgroundTokenRefreshCompleted = onBackgroundTokenRefreshCompleted;
+            return builder;
+        }
     }
 }

src/client/Microsoft.Identity.Client/Extensibility/ManagedIdentityApplicationBuilderExtensions.cs

@@ -0,0 +1,50 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System;
+using System.Threading.Tasks;
+
+namespace Microsoft.Identity.Client.Extensibility
+{
+    /// <summary>
+    /// Extensibility methods for <see cref="ManagedIdentityApplicationBuilder"/>.
+    /// </summary>
+#if !SUPPORTS_CONFIDENTIAL_CLIENT
+    [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)]  // hide managed identity flow on mobile
+#endif
+    public static class ManagedIdentityApplicationBuilderExtensions
+    {
+        /// <summary>
+        /// Configures an async callback invoked when a fire-and-forget background (proactive) token refresh completes.
+        /// Proactive refresh runs on a background thread after the caller has already received a valid cached token,
+        /// so its outcome (latency, failures) is otherwise unobservable. This callback surfaces it, e.g. for telemetry.
+        /// </summary>
+        /// <param name="builder">The managed identity application builder.</param>
+        /// <param name="onBackgroundTokenRefreshCompleted">
+        /// An async callback that receives the <see cref="ExecutionResult"/> of the background refresh. On success,
+        /// <see cref="ExecutionResult.Result"/> holds the refreshed token; on failure, <see cref="ExecutionResult.Exception"/>
+        /// holds the exception, whose <see cref="MsalException.AuthenticationResultMetadata"/> carries the failed
+        /// attempt's HTTP duration.
+        /// </param>
+        /// <returns>The builder to chain additional configuration calls.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="onBackgroundTokenRefreshCompleted"/> is null.</exception>
+        /// <remarks>
+        /// <para>Invoked on a background thread. Check <see cref="ExecutionResult.Successful"/> to determine the outcome.</para>
+        /// <para>Exceptions thrown by this callback are caught and logged internally so they cannot disrupt the refresh.</para>
+        /// </remarks>
+        public static ManagedIdentityApplicationBuilder OnBackgroundTokenRefreshCompleted(
+            this ManagedIdentityApplicationBuilder builder,
+            Func<ExecutionResult, Task> onBackgroundTokenRefreshCompleted)
+        {
+            builder.ValidateUseOfExperimentalFeature();
+
+            if (onBackgroundTokenRefreshCompleted == null)
+            {
+                throw new ArgumentNullException(nameof(onBackgroundTokenRefreshCompleted));
+            }
+
+            builder.Config.OnBackgroundTokenRefreshCompleted = onBackgroundTokenRefreshCompleted;
+            return builder;
+        }
+    }
+}

src/client/Microsoft.Identity.Client/Internal/Requests/RequestBase.cs

@@ -293,7 +293,7 @@ private void UpdateTelemetry(long elapsedMilliseconds, ApiEvent apiEvent, Authen
         /// is left at its default (0 / null). <see cref="AuthenticationResultMetadata.TokenSource"/> has
         /// no meaningful value on failure, so it stays at the constructor default and should not be relied on.
         /// </summary>
-        private static AuthenticationResultMetadata CreateFailureMetadata(ApiEvent apiEvent, long totalDurationInMs)
+        internal static AuthenticationResultMetadata CreateFailureMetadata(ApiEvent apiEvent, long totalDurationInMs)
         {
             return new AuthenticationResultMetadata(TokenSource.IdentityProvider)
             {

src/client/Microsoft.Identity.Client/Internal/Requests/SilentRequestHelper.cs

@@ -98,12 +98,13 @@ internal static void ProcessFetchInBackground(
                 try
                 {
                     var authResult = await fetchAction().ConfigureAwait(false);
+                    var executionResult = new ExecutionResult { Successful = true, Result = authResult };
 
                     // Invoke the enricher once for this background refresh and reuse the materialized
                     // tags across every instrument below.
                     IReadOnlyList<KeyValuePair<string, object>> extraTags = OtelEnrichmentHelper.MaterializeExtraTags(
                         tagsEnricher,
-                        () => new ExecutionResult { Successful = true, Result = authResult },
+                        () => executionResult,
                         logger);
 
                     serviceBundle.PlatformProxy.OtelInstrumentation.IncrementSuccessCounter(
@@ -135,6 +136,8 @@ internal static void ProcessFetchInBackground(
                         authResult.AuthenticationResultMetadata,
                         logger,
                         extraTags);
+
+                    await InvokeBackgroundRefreshCallbackAsync(serviceBundle, executionResult, logger).ConfigureAwait(false);
                 }
                 catch (MsalServiceException ex)
                 {
@@ -150,22 +153,66 @@ internal static void ProcessFetchInBackground(
 
                     LogBackgroundFailureTelemetry(serviceBundle, apiEvent, callerSdkId, callerSdkVersion,
                         ex.ErrorCode, ex.StatusCode, ex.ErrorCodes?.FirstOrDefault(), ex, tagsEnricher, logger);
+
+                    // Background refresh doesn't go through RunAsync, so the exception isn't carrying metadata yet.
+                    // Fill it in from apiEvent so the callback can see the HTTP duration and cache-refresh reason.
+                    // Total duration stays 0 on purpose - the caller already got a token from the cache.
+                    if (ex.AuthenticationResultMetadata == null)
+                    {
+                        ex.AuthenticationResultMetadata = RequestBase.CreateFailureMetadata(apiEvent, totalDurationInMs: 0);
+                    }
+
+                    await InvokeBackgroundRefreshCallbackAsync(serviceBundle, new ExecutionResult { Successful = false, Exception = ex }, logger).ConfigureAwait(false);
                 }
                 catch (OperationCanceledException ex)
                 {
                     logger.WarningPiiWithPrefix(ex, ProactiveRefreshCancellationError);
                     LogBackgroundFailureTelemetry(serviceBundle, apiEvent, callerSdkId, callerSdkVersion,
                         ex.GetType().Name, httpStatusCode: 0, tagsEnricher: tagsEnricher, logger: logger);
+
+                    await InvokeBackgroundRefreshCallbackAsync(serviceBundle, new ExecutionResult { Successful = false, Exception = null }, logger).ConfigureAwait(false);
                 }
                 catch (Exception ex)
                 {
                     logger.ErrorPiiWithPrefix(ex, ProactiveRefreshGeneralError);
                     LogBackgroundFailureTelemetry(serviceBundle, apiEvent, callerSdkId, callerSdkVersion,
                         ex.GetType().Name, httpStatusCode: 0, tagsEnricher: tagsEnricher, logger: logger);
+
+                    MsalException msalException = ex as MsalException;
+                    if (msalException != null && msalException.AuthenticationResultMetadata == null)
+                    {
+                        msalException.AuthenticationResultMetadata = RequestBase.CreateFailureMetadata(apiEvent, totalDurationInMs: 0);
+                    }
+
+                    await InvokeBackgroundRefreshCallbackAsync(serviceBundle, new ExecutionResult { Successful = false, Exception = msalException }, logger).ConfigureAwait(false);
                 }
             });
         }
 
+        // Invokes the app-configured background-refresh completion callback (confidential client and managed
+        // identity only). Runs on the fire-and-forget background thread; a throwing callback is caught and
+        // logged so it cannot disrupt the refresh.
+        private static async Task InvokeBackgroundRefreshCallbackAsync(
+            IServiceBundle serviceBundle,
+            ExecutionResult executionResult,
+            ILoggerAdapter logger)
+        {
+            Func<ExecutionResult, Task> callback = serviceBundle.Config.OnBackgroundTokenRefreshCompleted;
+            if (callback == null)
+            {
+                return;
+            }
+
+            try
+            {
+                await callback(executionResult).ConfigureAwait(false);
+            }
+            catch (Exception ex)
+            {
+                logger.WarningPiiWithPrefix(ex, "OnBackgroundTokenRefreshCompleted callback threw an exception; it was suppressed.");
+            }
+        }
+
         // Records telemetry for a fire-and-forget background refresh failure: increments the
         // failure counter and records V2 HTTP duration when an HTTP exchange happened.
         // Total duration is deliberately not recorded — the foreground user already received

src/client/Microsoft.Identity.Client/PublicApi/net462/PublicAPI.Unshipped.txt

@@ -6,3 +6,6 @@ Microsoft.Identity.Client.AppConfig.PoPOptions.PoPOptions() -> void
 static Microsoft.Identity.Client.Extensibility.AcquireTokenParameterBuilderExtensions.WithCachePartitionKey<T>(this Microsoft.Identity.Client.BaseAbstractAcquireTokenParameterBuilder<T> builder, string key, string value, bool partitionRefreshToken) -> T
 static Microsoft.Identity.Client.ManagedIdentityPopExtensions.WithMtlsProofOfPossession(this Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder builder, Microsoft.Identity.Client.AppConfig.PoPOptions options) -> Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder
 Microsoft.Identity.Client.MsalException.AuthenticationResultMetadata.get -> Microsoft.Identity.Client.AuthenticationResultMetadata
+Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions
+static Microsoft.Identity.Client.Extensibility.ConfidentialClientApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ConfidentialClientApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ConfidentialClientApplicationBuilder
+static Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ManagedIdentityApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ManagedIdentityApplicationBuilder

src/client/Microsoft.Identity.Client/PublicApi/net472/PublicAPI.Unshipped.txt

@@ -6,3 +6,6 @@ Microsoft.Identity.Client.AppConfig.PoPOptions.PoPOptions() -> void
 static Microsoft.Identity.Client.Extensibility.AcquireTokenParameterBuilderExtensions.WithCachePartitionKey<T>(this Microsoft.Identity.Client.BaseAbstractAcquireTokenParameterBuilder<T> builder, string key, string value, bool partitionRefreshToken) -> T
 static Microsoft.Identity.Client.ManagedIdentityPopExtensions.WithMtlsProofOfPossession(this Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder builder, Microsoft.Identity.Client.AppConfig.PoPOptions options) -> Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder
 Microsoft.Identity.Client.MsalException.AuthenticationResultMetadata.get -> Microsoft.Identity.Client.AuthenticationResultMetadata
+Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions
+static Microsoft.Identity.Client.Extensibility.ConfidentialClientApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ConfidentialClientApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ConfidentialClientApplicationBuilder
+static Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ManagedIdentityApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ManagedIdentityApplicationBuilder

src/client/Microsoft.Identity.Client/PublicApi/net8.0-android/PublicAPI.Unshipped.txt

@@ -6,3 +6,6 @@ Microsoft.Identity.Client.AppConfig.PoPOptions.PoPOptions() -> void
 static Microsoft.Identity.Client.Extensibility.AcquireTokenParameterBuilderExtensions.WithCachePartitionKey<T>(this Microsoft.Identity.Client.BaseAbstractAcquireTokenParameterBuilder<T> builder, string key, string value, bool partitionRefreshToken) -> T
 static Microsoft.Identity.Client.ManagedIdentityPopExtensions.WithMtlsProofOfPossession(this Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder builder, Microsoft.Identity.Client.AppConfig.PoPOptions options) -> Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder
 Microsoft.Identity.Client.MsalException.AuthenticationResultMetadata.get -> Microsoft.Identity.Client.AuthenticationResultMetadata
+Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions
+static Microsoft.Identity.Client.Extensibility.ConfidentialClientApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ConfidentialClientApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ConfidentialClientApplicationBuilder
+static Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ManagedIdentityApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ManagedIdentityApplicationBuilder

src/client/Microsoft.Identity.Client/PublicApi/net8.0-ios/PublicAPI.Unshipped.txt

@@ -6,3 +6,6 @@ Microsoft.Identity.Client.AppConfig.PoPOptions.PoPOptions() -> void
 static Microsoft.Identity.Client.Extensibility.AcquireTokenParameterBuilderExtensions.WithCachePartitionKey<T>(this Microsoft.Identity.Client.BaseAbstractAcquireTokenParameterBuilder<T> builder, string key, string value, bool partitionRefreshToken) -> T
 static Microsoft.Identity.Client.ManagedIdentityPopExtensions.WithMtlsProofOfPossession(this Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder builder, Microsoft.Identity.Client.AppConfig.PoPOptions options) -> Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder
 Microsoft.Identity.Client.MsalException.AuthenticationResultMetadata.get -> Microsoft.Identity.Client.AuthenticationResultMetadata
+Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions
+static Microsoft.Identity.Client.Extensibility.ConfidentialClientApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ConfidentialClientApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ConfidentialClientApplicationBuilder
+static Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ManagedIdentityApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ManagedIdentityApplicationBuilder

src/client/Microsoft.Identity.Client/PublicApi/net8.0/PublicAPI.Unshipped.txt

@@ -6,3 +6,6 @@ Microsoft.Identity.Client.AppConfig.PoPOptions.PoPOptions() -> void
 static Microsoft.Identity.Client.Extensibility.AcquireTokenParameterBuilderExtensions.WithCachePartitionKey<T>(this Microsoft.Identity.Client.BaseAbstractAcquireTokenParameterBuilder<T> builder, string key, string value, bool partitionRefreshToken) -> T
 static Microsoft.Identity.Client.ManagedIdentityPopExtensions.WithMtlsProofOfPossession(this Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder builder, Microsoft.Identity.Client.AppConfig.PoPOptions options) -> Microsoft.Identity.Client.AcquireTokenForManagedIdentityParameterBuilder
 Microsoft.Identity.Client.MsalException.AuthenticationResultMetadata.get -> Microsoft.Identity.Client.AuthenticationResultMetadata
+Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions
+static Microsoft.Identity.Client.Extensibility.ConfidentialClientApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ConfidentialClientApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ConfidentialClientApplicationBuilder
+static Microsoft.Identity.Client.Extensibility.ManagedIdentityApplicationBuilderExtensions.OnBackgroundTokenRefreshCompleted(this Microsoft.Identity.Client.ManagedIdentityApplicationBuilder builder, System.Func<Microsoft.Identity.Client.Extensibility.ExecutionResult, System.Threading.Tasks.Task> onBackgroundTokenRefreshCompleted) -> Microsoft.Identity.Client.ManagedIdentityApplicationBuilder