Allow usage of relative URIs in AuthnContextClassRef

[glatzert]

Allow usage of relative URIs in AuthnContextClassRef

Introduces a AppContext switch, that allows to cirumvent a condition that checks for Uri.IsAbsoulte on Saml2AuthenticationContext.ClassReference

Fixes #3279

@brentschmaltz

[Copilot]

Pull Request Overview

This PR introduces a new AppContext switch to allow relative URIs in SAML2 AuthnContextClassRef elements. Currently, the library enforces that ClassReference values must be absolute URIs, but this change provides a configuration option to bypass this validation when needed.

• Adds a new AppContext switch AllowRelativeUrisInSaml2AuthnContext to control URI validation behavior
• Modifies the Saml2AuthenticationContext.ClassReference setter to conditionally allow relative URIs
• Includes comprehensive test coverage with proper test isolation through collection definitions

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
AppContextSwitches.cs	Adds the new switch definition and reset logic
Saml2AuthenticationContext.cs	Updates ClassReference validation to respect the new switch
Saml2AuthenticationContextWithAppContextTests.cs	New test file to verify the switch functionality
Saml2AuthenticationContextTests.cs	Adds collection attribute for test isolation
Saml2AuthenticationContextCollectionDefinition.cs	Defines test collection with disabled parallelization

[pmaytak]

Once this is released, we'll need to update: https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet/wiki/App-Context-Switches-in-IdentityModel

[glatzert]

I updated the suggestions and rebased as per Githubs request - I hope I did not break anything in your workflow by doing that 🙈

I was sick last week, so I needed a liitle bit.
Nevertheless I found one thing about the test cases - if they run in Visual Studio simultanously for each .net version, some will fail - I think the xunit runner does not isolate the AppContext against each other in that case. Running the tests for a single .net version will work as expected.

[glatzert]

Can I do something about the (probably) shared AppContext in the different dotnet versions or did i miss something in older .net runtimes?