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

[Copilot]

Managed identity auth failures surface a host-issued correlation ID, but neither the error message nor the request-failure log identified which managed identity source (AppService, Imds, ServiceFabric, etc.) produced it — making live-site triage ambiguous across host telemetry systems.

Changes proposed in this request

• AbstractManagedIdentity.cs

  • Request-failure log line now includes _sourceType:

    [Managed Identity] request failed, Source: AppService, HttpStatusCode: 500 Error message: ...
    

  • Correlation ID message now attributes the ID to the specific host:

    Managed Identity Correlation ID: <id> (issued by the 'AppService' managed identity source; search that source's telemetry with this correlation ID). Use this Correlation ID for further investigation.
    

  • Source is taken from the existing _sourceType field — no hardcoding, reflects the host detected at runtime.

• CHANGELOG.md — added ### Changes entry under the in-progress version.

Testing

• Updated two [DataRow] entries in ManagedIdentityTestErrorResponseParsing to assert the new source attribution phrase appears in the error message for correlation-ID-bearing responses.
• Added ManagedIdentityErrorMessageAttributesCorrelationIdToSourceAsync — parametrized over AppService and Imds sources — to guard the correlation-ID attribution branch against regression across non-AppService sources. Asserts the full composed phrase (not just the source name) to prevent false passes from echoed error bodies.

No behavioral or auth changes — message/log content only. No public API surface changes.

Performance impact

None — string interpolation on an already-allocated error path.

Documentation

• All relevant documentation is updated.

Co-authored-by: juliovi-1 126522119+juliovi-1@users.noreply.github.com

[Copilot]

Pull request overview

This PR improves managed identity failure diagnostics by including the detected ManagedIdentitySource (e.g., AppService, Imds) in both request-failure logs and correlation-ID-bearing error messages, making it easier to route the host-issued correlation ID to the correct telemetry system during incident triage.

Changes:

• Added managed identity source information to the managed identity “request failed” log line.
• Enhanced correlation-ID error message text to attribute the correlation ID to the detected managed identity source.
• Updated/added unit tests to assert the new attribution text for both AppService and IMDS sources, and documented the change in the changelog.

Reviewed changes

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

File	Description
tests/Microsoft.Identity.Test.Unit/ManagedIdentityTests/ManagedIdentityTests.cs	Updates existing parsing assertions and adds a new parametrized regression test to validate correlation-ID attribution across MI sources.
src/client/Microsoft.Identity.Client/ManagedIdentity/AbstractManagedIdentity.cs	Includes _sourceType in the failure log and in the correlation-ID error-message branch.
CHANGELOG.md	Documents the diagnostic-message/log enhancement under the current version section.

[bgavrilMS]

Doesn't preserve attribution.

[Robbie-Microsoft]

Superseded by #6101, which carries @juliovi-1's original commits cherry-picked unchanged so he remains the git author (this PR rewrote the code and did not preserve authorship). Closing in favor of #6101.