Respond to IL2026 warnings in DataProtection originating from EncryptedXml

[eerhardt]

With dotnet/runtime#84468, EncryptedXml is now marked as RequiresUnreferencedCode. This is because

The algorithm implementations referenced in the XML payload might be removed. Ensure the required algorithm implementations are preserved in your application.

From discussion in #47410 (comment), we should:

1. Figure out the list of commonly used crypto algorithms used by DataProtection, and add [DynamicDependency] attributes for them.
2. We also add some trimming/aot tests to ensure DataProtection works correctly when trimmed.
3. DataProtection then suppresses the warnings coming from System.Security.Cryptography.Xml

[blowdart]

Good luck :)

https://learn.microsoft.com/en-us/aspnet/core/security/data-protection/configuration/default-settings?view=aspnetcore-7.0

So the defaults are AES-256-CBC and HMACSHA256 however EncryptedXml is nicely flexible, so any hmac and any symmetric key algorithm is possible.

What you probably want as a starting point is anything that can be configured with the easy access settings,

https://learn.microsoft.com/en-us/aspnet/core/security/data-protection/configuration/overview?view=aspnetcore-7.0#changing-algorithms-with-usecryptographicalgorithms

Which ends up being https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.dataprotection.authenticatedencryption.configurationmodel.authenticatedencryptorconfiguration?view=aspnetcore-7.0

For encryption it's only AES without a bunch of work,

https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.dataprotection.authenticatedencryption.encryptionalgorithm?view=aspnetcore-7.0

For validation it's only HMAC256 and HMAC512

https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.dataprotection.authenticatedencryption.validationalgorithm?view=aspnetcore-7.0

[eerhardt]

Note: when doing this work, we should remove the RequiresUnreferencedCode attribute that was added to AddAuthentication() in #47663.

aspnetcore/src/Security/Authentication/Core/src/AuthenticationServiceCollectionExtensions.cs

Lines 20 to 21 in 5807400

	[RequiresUnreferencedCode("Authentication middleware does not currently support native AOT.", Url = "https://aka.ms/aspnet/nativeaot")]
	public static AuthenticationBuilder AddAuthentication(this IServiceCollection services)