Expose cert used in mtls flows in the auth result

[gladjohn]

Fixes #5370

Changes proposed in this request
This pull request introduces several updates to the Microsoft.Identity.Client library, focusing on adding support for binding certificates in mTLS-PoP scenarios, improving the AuthenticationResult API, and enhancing test coverage. Key changes include the addition of a BindingCertificate property, modifications to property access levels, and updates to unit and integration tests to validate the new functionality.

Updates to AuthenticationResult API:

• Added a new BindingCertificate property to AuthenticationResult for mTLS-PoP token scenarios. This property allows binding an X509 certificate to access tokens. (src/client/Microsoft.Identity.Client/AuthenticationResult.cs - [1] [2]
• Changed several properties in AuthenticationResult (e.g., UniqueId, ExpiresOn, TenantId, Account, etc.) to internal set to enable modification within the library while maintaining encapsulation. (src/client/Microsoft.Identity.Client/AuthenticationResult.cs - [1] [2] [3]
• Marked constructors in AuthenticationResult as obsolete to discourage direct use and encourage usage of factory methods or builders. (src/client/Microsoft.Identity.Client/AuthenticationResult.cs - [1] [2]

Integration of mTLS-PoP functionality:

• Updated MtlsPopAuthenticationOperation to set the BindingCertificate property in AuthenticationResult during the token acquisition process. (src/client/Microsoft.Identity.Client/AuthScheme/PoP/MtlsPopAuthenticationOperation.cs - src/client/Microsoft.Identity.Client/AuthScheme/PoP/MtlsPopAuthenticationOperation.csL41-R41)
• Added API references for the new BindingCertificate property across various platform-specific PublicAPI.Unshipped.txt files. (src/client/Microsoft.Identity.Client/PublicApi/*/PublicAPI.Unshipped.txt - src/client/Microsoft.Identity.Client/PublicApi/net462/PublicAPI.Unshipped.txtR3)

Test enhancements:

• Added integration tests to validate the BindingCertificate functionality in mTLS-PoP scenarios, ensuring the certificate is correctly set and retrieved from cache during token acquisition. (tests/Microsoft.Identity.Test.Integration.netcore/HeadlessTests/ClientCredentialsMtlsPopTests.cs - [1] [2]
• Updated unit tests to include assertions for the BindingCertificate property and deprecated constructor usage warnings. (tests/Microsoft.Identity.Test.Unit/PublicApiTests/AuthenticationResultTests.cs - [1] [2] [3]
• Enhanced mTLS-PoP unit tests to verify the presence and correctness of the BindingCertificate in cached and non-cached scenarios. (tests/Microsoft.Identity.Test.Unit/PublicApiTests/MtlsPopTests.cs - [1] [2]

These changes collectively improve the library's support for mTLS-PoP scenarios, enhance API usability, and ensure robust test coverage for the new functionality.

Testing
unit and integration

Performance impact
none

Documentation

• All relevant documentation is updated.

[gladjohn]

@neha-bhargava @trwalke @bgavrilMS , need suggestion on how to fix the failing tests - PublicTestConstructorCoversAllProperties

test fails with,

Assert.AreEqual failed. Expected:<15>. Actual:<16>. The constructor should include all properties of AuthenticationObject

but if I add the property to the test ctor, and update the public API, then I get this,

Symbol 'AuthenticationResult' violates the backcompat requirement: 'Do not add multiple overloads with optional parameters'. See 'https://github.com/dotnet/roslyn/blob/main/docs/Adding%20Optional%20Parameters%20in%20Public%20API.md' for details.

[gladjohn]

@neha-bhargava @trwalke @bgavrilMS , need suggestion on how to fix the failing tests - PublicTestConstructorCoversAllProperties

test fails with,

Assert.AreEqual failed. Expected:<15>. Actual:<16>. The constructor should include all properties of AuthenticationObject

but if I add the property to the test ctor, and update the public API, then I get this,

Symbol 'AuthenticationResult' violates the backcompat requirement: 'Do not add multiple overloads with optional parameters'. See 'https://github.com/dotnet/roslyn/blob/main/docs/Adding%20Optional%20Parameters%20in%20Public%20API.md' for details.

i have a fix for this, hopefully not breaking any public APIs, please review carefully.

[bgavrilMS]

No need for new integration test