WebAuthnAuthenticationProvider does not pass UserDetails to WebAuthnAuthentication

Describe the bug
WebAuthnAuthenticationProvider creates a WebAuthnAuthentication with a principal of type PublicKeyCredentialUserEntity instead of UserDetails.

https://github.com/spring-projects/spring-security/blob/7.0.0-RC1/webauthn/src/main/java/org/springframework/security/web/webauthn/authentication/WebAuthnAuthenticationProvider.java#L77

To Reproduce

• authenticate via webauthn
• check SecurityContext.getAuthentication().getPrincipal() - it is an ImmutablePublicKeyCredentialUserEntity

Expected behavior
The retrieved UserDetails instance should be used as principal of the created WebAuthnAuthentication (WebAuthnAuthenticationProvider javadoc looks correct).

Sample

sample app will be referenced asap:

• run
• http://localhost:8080/login - user / password
• http://localhost:8080/webauthn/register - register a passkey
• http://localhost:8080/logout
• http://localhost:8080/login - use passkey
• check debug console log

2025-10-27T15:19:44.309+01:00 DEBUG 40608 --- [demo] [nio-8080-exec-2] o.s.s.w.w.a.WebAuthnAuthenticationFilter : Set SecurityContextHolder to WebAuthnAuthentication [Principal=org.springframework.security.web.webauthn.api.ImmutablePublicKeyCredentialUserEntity@205490ff, Credentials=[PROTECTED], Authenticated=true, Details=null, Granted Authorities=[ROLE_USER, FactorGrantedAuthority [authority=FACTOR_WEBAUTHN, issuedAt=2025-10-27T14:19:42.009552700Z]]]

Start at webauthn/src/main/java/org/springframework/security/web/webauthn/authentication/WebAuthnAuthenticationProvider.java around line 77 and trace the authentication flow described in the issue. Reproduce the WebAuthn login, inspect SecurityContext.getAuthentication().getPrincipal(), and consider the issue complete when it is the retrieved UserDetails instance rather than an ImmutablePublicKeyCredentialUserEntity.