Update MFA docs, ASP.NET Core now supports passkeys (#36567)

Author: damienbod

aspnetcore/security/authentication/mfa.md

@@ -56,7 +56,7 @@ passkeys/FIDO2 is currently:
 * The most secure way of achieving MFA.
 * MFA that protects against phishing attacks. (As well as certificate authentication and Windows for business)
 
-At present, ASP.NET Core doesn't support passkeys/FIDO2 directly. Passkeys/FIDO2 can be used for MFA or passwordless flows.
+ASP.NET Core supports passkeys using ASP.NET Core Identity. Passkeys/FIDO2 can be used for MFA or passwordless flows. For more information, see <xref:security/authentication/passkeys/index>.
 
 Microsoft Entra ID provides support for passkeys/FIDO2 and passwordless flows. For more information, see [Passwordless authentication options](/azure/active-directory/authentication/concept-authentication-passwordless).