[12.0 P1] Document new .NET 12 passkey features

[rolandVi]

Description

Unblocks when aspnetcore-12.0 exists on Learn.

What needs documenting

Three features already merged into dotnet/aspnetcore main. All for .NET 12.

1. Well-known passkey endpoints (Add serving of .well-known/passkey-endpoints to Identity aspnetcore#68066). AddPasskeyEndpoints and MapWellKnownPasskeyEndpoints serve a discovery document at /.well-known/passkey-endpoints. Marked [Experimental("ASP0039")], which is a compile error and not a warning, so the suppression guidance has to be part of the docs. Mapping under a route group prefix logs an error rather than throwing.
2. WebAuthn signals API (Support the WebAuthn signals API for passkeys aspnetcore#68129). Three SignInManager methods plus matching IPasskeyHandler<TUser> default interface members. The security points that need to survive into the prose: the browser treats the accepted-credentials list as authoritative, so an incomplete list permanently deletes working passkeys, and signalUnknownCredential also deletes permanently, which is why the method returns null on anything inconclusive.
3. Reauthentication before adding a passkey (Require reauthentication before adding a passkey or setting a password aspnetcore#68522). Template only, no new public API, but it moves /Account/PasskeyCreationOptions to /Account/Manage/PasskeyCreationOptions and adds PasskeyOperation.Reauthenticate.

The content

The finished draft is the diff on #37565, 116 lines against index.md. It should still apply once the moniker exists, though every API name is worth rechecking against PublicAPI first.

Page URL

https://learn.microsoft.com/en-us/aspnet/core/security/authentication/passkeys/?view=aspnetcore-10.0

Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/security/authentication/passkeys/index.md

Document ID

f44a13ca-c7a0-490a-9251-931ff16554f2

Platform Id

c5da9dfd-32c6-e966-5a91-9426d957e69f

Article author

@guardrex

Metadata

• ID: f44a13ca-c7a0-490a-9251-931ff16554f2
• PlatformId: c5da9dfd-32c6-e966-5a91-9426d957e69f
• Service: aspnet-core
• Sub-service: security

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