Include ManagedIdentitySource in managed identity error messages and request-failure logs

[juliovi-1]

Summary

Managed identity authentication failures surface a host-issued Managed Identity Correlation ID, but neither the customer-facing error message nor the request-failure log indicated which managed identity source (AppService, Imds, ServiceFabric, AzureArc, CloudShell, MachineLearning, etc.) produced that correlation ID. During live-site investigations this is ambiguous: each host emits its correlation ID into its own telemetry, so without the source you don't know which host's telemetry to search.

This change appends the detected ManagedIdentitySource to:

• the request-failure log line ([Managed Identity] request failed, Source: {source}, ...), and
• the customer-facing correlation ID message, clarifying that the correlation ID should be searched in that source's telemetry.

The source is taken from the existing _sourceType value already known to AbstractManagedIdentity at runtime — it is not hardcoded; the value reflects the host detected at runtime.

Motivation

We recently root-caused a ManagedIdentityCredential authentication failed incident where the failure originated in the host (App Service) with an AADSTS500011 resource-principal-not-found error. The host-issued correlation ID was present, but the exception did not say it came from the App Service host, slowing down the investigation. Surfacing the source makes the correlation ID directly actionable.

Changes

• AbstractManagedIdentity.cs: include _sourceType in the request-failure log line and in the correlation ID message (only when a host correlation ID is present).
• ManagedIdentityTests.cs: updated ManagedIdentityTestErrorResponseParsing rows that carry a host correlationId to assert the source (AppService) and the new explanatory text appear in the message.
• CHANGELOG.md: added a ### Changes entry under the in-progress version.

Testing

• ManagedIdentityTestErrorResponseParsing — all rows pass.
• ManagedIdentityTestWrongScopeAsync (cross-source regression coverage) — passes.
• Local build of Microsoft.Identity.Client is clean; no public API surface changes.

Notes

• No behavioral/auth changes — message/log content only.
• The CHANGELOG link placeholder will be updated with this PR number.

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[Copilot]

Pull request overview

This PR improves managed identity diagnostics by including the detected ManagedIdentitySource in both request-failure logs and customer-facing error messages when a host-issued managed identity correlation ID is present, making correlation IDs actionable during live-site investigations.

Changes:

• Added ManagedIdentitySource to the managed identity request-failure error log line.
• Appended ManagedIdentitySource context to the “Managed Identity Correlation ID” portion of the error message (when correlation ID is present).
• Updated unit tests and changelog entry to reflect the new message/log content.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/client/Microsoft.Identity.Client/ManagedIdentity/AbstractManagedIdentity.cs	Adds _sourceType to request-failure logging and correlation-ID error message text.
tests/Microsoft.Identity.Test.Unit/ManagedIdentityTests/ManagedIdentityTests.cs	Updates expected substrings in parsing tests to assert the new source/context text.
CHANGELOG.md	Documents the diagnostic message/log enhancement under the in-progress release section.