Add | Add FIC + MSI support

[yhvicey]

Resolves #2556.

This PR adds support for authenticating Azure SQL Server using federated identity credentials (FIC) and managed identity (MSI). It provides similar functionality as the ActiveDirectoryWorkloadIdentity, but supports using managed identity directly.

It will use values from below environments to finish authentication process:

• AZURE_CLIENT_ID, the client id of multi-tenant Microsoft Entra App id, may be overridden by User Id.
• AZURE_TENANT_ID, the tenant id where target resource locates.
• AZURE_MSI_CLIENT_ID, the client id of managed identity.

Note: The first two environment variables are defined in Azure.Identity library, the third one is newly defined.

[David-Engel]

Just a couple notes for now.

[codecov]

Codecov Report

Attention: Patch coverage is 37.83784% with 46 lines in your changes missing coverage. Please review.

Project coverage is 71.71%. Comparing base (f7ab115) to head (f43f52c).
Report is 50 commits behind head on main.

Files	Patch %	Lines
...SqlClient/ActiveDirectoryAuthenticationProvider.cs	7.89%	35 Missing ⚠️
...nt/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs	0.00%	4 Missing ⚠️
.../netcore/src/Microsoft/Data/SqlClient/TdsParser.cs	0.00%	2 Missing ⚠️
...ent/SqlAuthenticationProviderManager.NetCoreApp.cs	0.00%	1 Missing ⚠️
...core/src/Microsoft/Data/SqlClient/SqlConnection.cs	85.71%	1 Missing ⚠️
...Data/SqlClient/SqlAuthenticationProviderManager.cs	50.00%	1 Missing ⚠️
...etfx/src/Microsoft/Data/SqlClient/SqlConnection.cs	85.71%	1 Missing ⚠️
...rc/Microsoft/Data/SqlClient/SqlConnectionString.cs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2557      +/-   ##
==========================================
- Coverage   72.81%   71.71%   -1.11%     
==========================================
  Files         311      308       -3     
  Lines       61694    62374     +680     
==========================================
- Hits        44922    44730     -192     
- Misses      16772    17644     +872     

Flag	Coverage Δ
addons	92.88% <ø> (ø)
netcore	75.89% <31.03%> (-1.29%)	⬇️
netfx	69.72% <32.25%> (-0.73%)	⬇️

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[yhvicey]

Shall we use ActiveDirectoryFederatedIdentityCredentials, or ActiveDirectoryFederatedIdentity?

[srxmsft]

Since it might take some time for this PR to be release to Microsoft.Data.SqlClient.
For the cross tenant FIC scenario, do you suggest to manually set AccessToken or AccessTokenCallback as of now?
Is there any example we can follow?

[yhvicey]

If you're looking for a temporary workaround/solution, ping @yiwwan at Teams, I'll share workaround solution.

[DavoudEshtehari]

@yhvicey I couldn't find the AZURE_MSI_CLIENT_ID environment variable in the documentation or the source code. I might be looking in the wrong places; could you please provide me with the correct links?

[yhvicey]

@DavoudEshtehari it's not official env var used by azure.identity (see PR's description), I also worried about what if azure.identity added support for MSI + FIC in the future and didn't use same env var name. Maybe we can switch to a ADO.NET specific env var name.
Or, we can add MSI + FIC in azure.identity first, then leverage it here directly, but that'll took much longer time, I expect

[DavoudEshtehari]

@DavoudEshtehari it's not official env var used by azure.identity (see PR's description), I also worried about what if azure.identity added support for MSI + FIC in the future and didn't use same env var name. Maybe we can switch to a ADO.NET specific env var name. Or, we can add MSI + FIC in azure.identity first, then leverage it here directly, but that'll took much longer time, I expect

We usually don't accept unofficial dependencies to avoid the breaking changes.
cc @saurabh500 @David-Engel

[cheenamalhotra]

Note: The first two environment variables are defined in Azure.Identity library, the third one is newly defined.

What is the plan to document this new env variable? If this is something that will take time, I would recommend converting this PR to draft or closing if this is not in plan. But the driver only consumes documented APIs, or will not expose a feature until the behavior is documented use of the same.