Expose canonical tag names per-metric

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

@@ -0,0 +1,171 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using Microsoft.Identity.Client.TelemetryCore;
+
+namespace Microsoft.Identity.Client.Extensibility
+{
+    /// <summary>
+    /// Describes the OpenTelemetry metrics that MSAL emits and, for each metric, the canonical
+    /// (MSAL-owned) tag names it records. Consumers such as downstream metric pipelines can use
+    /// <see cref="CanonicalTagsByMetric"/> to discover which tags belong to a given MSAL metric and,
+    /// for example, keep only those tags.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// The tag names listed for a metric are the canonical base tags MSAL emits for it (some are conditional). They do not
+    /// include any extra tags supplied through
+    /// <see cref="AbstractConfidentialClientAcquireTokenParameterBuilderExtension.WithOtelTagsEnricher{T}"/>,
+    /// which are caller-defined and therefore not part of this catalog. Some canonical tags are emitted only
+    /// under certain conditions (for example the raw STS error-code tag is present on the failure counter only
+    /// when the STS returns a sub-error); they are listed here because they are part of the metric's canonical
+    /// schema.
+    /// </para>
+    /// <para>
+    /// Both the metric names (the dictionary keys) and the tag names (the dictionary values) are plain strings
+    /// that match what MSAL records, so consumers can compare them directly against the metric and tag names
+    /// observed on the OpenTelemetry pipeline, then drive per-metric tag filtering from this mapping (for
+    /// example via OpenTelemetry Views and <c>MetricStreamConfiguration.TagKeys</c>). Keeping the mapping here
+    /// means it stays in sync with MSAL automatically: updating the MSAL package reference updates the canonical
+    /// tag set, with nothing to maintain on the consumer side.
+    /// </para>
+    /// </remarks>
+    public static class MsalMetricsCatalog
+    {
+        // Metric names are defined once here (internal) so the published catalog and the instruments created in
+        // OtelInstrumentation share a single source of truth and cannot drift. They are intentionally not part of
+        // the public surface: consumers read metric names from the keys of CanonicalTagsByMetric (and from the
+        // OpenTelemetry pipeline), so there is no need to expose them as separate public constants.
+        internal const string SuccessCounterName = "MsalSuccess";
+        internal const string FailureCounterName = "MsalFailure";
+        internal const string TotalDurationHistogramName = "MsalTotalDuration.1A";
+        internal const string TotalDurationV2HistogramName = "MsalTotalDurationV2.1A";
+        internal const string DurationInL1CacheHistogramName = "MsalDurationInL1CacheInUs.1B";
+        internal const string DurationInL2CacheHistogramName = "MsalDurationInL2Cache.1A";
+        internal const string DurationInHttpHistogramName = "MsalDurationInHttp.1A";
+        internal const string DurationInHttpV2HistogramName = "MsalDurationInHttpV2.1A";
+        internal const string DurationInExtensionHistogramName = "MsalDurationInExtensionInMs.1B";
+        internal const string RemainingTokenLifetimeHistogramName = "MsalRemainingTokenLifetime.1A";
+
+        /// <summary>
+        /// Maps each MSAL metric name to the read-only list of canonical tag names that metric records.
+        /// Keys are compared with <see cref="System.StringComparer.Ordinal"/>.
+        /// </summary>
+        public static IReadOnlyDictionary<string, IReadOnlyList<string>> CanonicalTagsByMetric { get; } =
+            BuildCanonicalTagsByMetric();
+
+        private static IReadOnlyDictionary<string, IReadOnlyList<string>> BuildCanonicalTagsByMetric()
+        {
+            // Tag names reference the internal TelemetryConstants used when recording, so the mapping cannot
+            // drift from the tags MSAL actually emits.
+            var map = new Dictionary<string, string[]>(StringComparer.Ordinal)
+            {
+                [SuccessCounterName] = new[]
+                {
+                    TelemetryConstants.MsalVersion,
+                    TelemetryConstants.Platform,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.CallerSdkId,
+                    TelemetryConstants.TokenSource,
+                    TelemetryConstants.CacheRefreshReason,
+                    TelemetryConstants.CacheLevel,
+                    TelemetryConstants.TokenType,
+                },
+                [FailureCounterName] = new[]
+                {
+                    TelemetryConstants.MsalVersion,
+                    TelemetryConstants.Platform,
+                    TelemetryConstants.ErrorCode,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.CallerSdkId,
+                    TelemetryConstants.CacheRefreshReason,
+                    TelemetryConstants.TokenType,
+                    TelemetryConstants.RawStsErrorCode,
+                },
+                [TotalDurationHistogramName] = new[]
+                {
+                    TelemetryConstants.MsalVersion,
+                    TelemetryConstants.Platform,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.TokenSource,
+                    TelemetryConstants.CacheLevel,
+                    TelemetryConstants.CacheRefreshReason,
+                    TelemetryConstants.TokenType,
+                },
+                [TotalDurationV2HistogramName] = new[]
+                {
+                    TelemetryConstants.MsalVersionPlatform,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.TokenSource,
+                    TelemetryConstants.CacheLevel,
+                    TelemetryConstants.CacheRefreshReason,
+                    TelemetryConstants.TokenType,
+                    TelemetryConstants.ErrorCode,
+                    TelemetryConstants.Succeeded,
+                },
+                [DurationInL1CacheHistogramName] = new[]
+                {
+                    TelemetryConstants.MsalVersion,
+                    TelemetryConstants.Platform,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.TokenSource,
+                    TelemetryConstants.CacheLevel,
+                    TelemetryConstants.CacheRefreshReason,
+                },
+                [DurationInL2CacheHistogramName] = new[]
+                {
+                    TelemetryConstants.MsalVersion,
+                    TelemetryConstants.Platform,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.CacheRefreshReason,
+                },
+                [DurationInHttpHistogramName] = new[]
+                {
+                    TelemetryConstants.MsalVersion,
+                    TelemetryConstants.Platform,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.TokenType,
+                },
+                [DurationInHttpV2HistogramName] = new[]
+                {
+                    TelemetryConstants.MsalVersionPlatform,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.TokenType,
+                    TelemetryConstants.HttpStatusCode,
+                },
+                [DurationInExtensionHistogramName] = new[]
+                {
+                    TelemetryConstants.MsalVersion,
+                    TelemetryConstants.Platform,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.TokenSource,
+                    TelemetryConstants.CacheLevel,
+                    TelemetryConstants.TokenType,
+                },
+                [RemainingTokenLifetimeHistogramName] = new[]
+                {
+                    TelemetryConstants.MsalVersionPlatform,
+                    TelemetryConstants.ApiId,
+                    TelemetryConstants.TokenSource,
+                    TelemetryConstants.CacheLevel,
+                    TelemetryConstants.CacheRefreshReason,
+                    TelemetryConstants.TokenType,
+                },
+            };
+
+            // Expose each tag list as a ReadOnlyCollection rather than the backing array: an IReadOnlyList that is
+            // actually a string[] can be cast back and mutated by a consumer, which would corrupt this shared
+            // static catalog process-wide. The dictionary itself is already read-only.
+            var readOnlyMap = new Dictionary<string, IReadOnlyList<string>>(map.Count, StringComparer.Ordinal);
+            foreach (KeyValuePair<string, string[]> entry in map)
+            {
+                readOnlyMap[entry.Key] = Array.AsReadOnly(entry.Value);
+            }
+
+            return new ReadOnlyDictionary<string, IReadOnlyList<string>>(readOnlyMap);
+        }
+    }
+}