[6.1] Fix SetProvider to return immediately if user-defined provider found

[cheenamalhotra]

Ports #3620 to release/6.1

[Copilot]

Pull Request Overview

This PR ports a fix to the SetProvider method in the SqlAuthenticationProviderManager to return immediately when a user-defined provider is found, preventing it from being replaced. The fix ensures that custom authentication providers configured via app.config files are preserved and not overridden by default providers.

Key changes:

• Modified SetProvider method to return false immediately when a user-defined provider exists
• Added comprehensive test coverage for app.config provider registration scenarios
• Enhanced documentation with comments about configuration file support limitations

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlAuthenticationProviderManager.cs	Core fix: changed break to return false to prevent overriding user-defined providers
src/Microsoft.Data.SqlClient/tests/FunctionalTests/app.config	Added test configuration to register a dummy authentication provider
src/Microsoft.Data.SqlClient/tests/FunctionalTests/DataCommon/DummySqlAuthenticationProvider.cs	Created dummy provider for testing app.config registration
src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlAuthenticationProviderTest.cs	Added test to verify user-defined provider is used instead of default
src/Microsoft.Data.SqlClient/tests/FunctionalTests/AADAuthenticationTests.cs	Added integration test to validate dummy provider functionality
src/Microsoft.Data.SqlClient/tests/FunctionalTests/Microsoft.Data.SqlClient.FunctionalTests.csproj	Updated project to include new files and copy app.config for .NET Framework builds

Comments suppressed due to low confidence (1)

src/Microsoft.Data.SqlClient/tests/FunctionalTests/DataCommon/DummySqlAuthenticationProvider.cs:1

• The assertion parameters are in the wrong order. In xUnit, the expected value should come first: Assert.Equal(DummySqlAuthenticationProvider.DUMMY_TOKEN_STR, token.AccessToken).

// Licensed to the .NET Foundation under one or more agreements.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.09%. Comparing base (7a7b54e) to head (547dfcb).
⚠️ Report is 13 commits behind head on release/6.1.

Additional details and impacted files

@@               Coverage Diff               @@
##           release/6.1    #3651      +/-   ##
===============================================
+ Coverage        69.69%   70.09%   +0.39%     
===============================================
  Files              281      279       -2     
  Lines            62413    61748     -665     
===============================================
- Hits             43500    43283     -217     
+ Misses           18913    18465     -448     

Flag	Coverage Δ
addons	90.82% <ø> (ø)
netcore	73.11% <0.00%> (+0.35%)	⬆️
netfx	69.79% <100.00%> (+0.55%)	⬆️

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