This section details on the original issue you should resolve

<issue_title>MVC Customize Identity Issue</issue_title>
<issue_description>### Description

Hi, I have been struggling with adding FirstName LastName custom data into an identityUser customization. Not looking for a detailed, response, but hi level. If I create a new project (MVC Framework 8, authentication type individuals) and started from there, should this work?
Do you have a tutorial that starts from there? Would be nice if not. been trying to do this for min 2-3 years, and I keep giving up because I never can get it to work.

Page URL

https://learn.microsoft.com/en-us/aspnet/core/security/authentication/add-user-data?view=aspnetcore-9.0&tabs=visual-studio

Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/security/authentication/add-user-data.md

Document ID

cd157d04-d596-83fa-6edb-24d52193eb34

Platform Id

6617dcc3-4828-8b6c-4b70-b2be2a7b9233

Article author

@wadepickett

Metadata

• ID: 431df4fc-4168-cc8f-d053-9b264d2971c1
• PlatformId: 6617dcc3-4828-8b6c-4b70-b2be2a7b9233
• Service: aspnet-core
• Sub-service: security

Related Issues</issue_description>

Comments on the Issue (you are @copilot in this section)

Issue Summary

This is a valid issue.

Developers often need to just add simple custom properties (FirstName, LastName) to an ASP.NET Core Identity user in a newly created MVC (.NET 8 / 9, Individual Accounts) project. The current article’s sample and narrative focus on a Razor Pages template (6.x-era) and only mentions that instructions are "similar" for MVC, without explicitly showing the modern MVC & Razor Pages templates, current dotnet new commands, or a concise high-level checklist. The article is dated (ms.date 03/15/2022), has no moniker section for .NET 7/8/9, and therefore appears stale. This creates friction for developers expecting direct, up-to-date guidance.

Decision: Introduce a new .NET 9 (current) sample (add-user-data/samples/9.x/SampleApp) and reuse it for .NET 8 by noting that the code is identical except for TargetFramework. This avoids creating a separate 8.x sample folder and keeps future maintenance minimal.

Scope Validation

Within article intent: Yes. The doc’s purpose is to show how to add, download, and delete custom user data with Identity. Adding explicit guidance for MVC, current versions, and a minimal property scenario (First/Last name) fits squarely within scope.

Target Framework / Tooling (Current vs. Document)

Document currently: monikers up to >=6.0 (lines 25–170 in existing version), plus older 3.x and 2.x sections.
Needed: Add >= aspnetcore-9.0 (primary), add >= aspnetcore-8.0 < aspnetcore-9.0 referencing the 9.x sample, retain/adjust >=6.0 <8.0 as legacy. Update ms.date.

Root Causes of User Difficulty

1. No explicit .NET 8/9 mention; perceived obsolescence.
2. Lack of explicit MVC template steps (dotnet new mvc -au Individual).
3. No quick-start "just add 2 properties" checklist.
4. Identity Razor Pages architecture not clearly reiterated for MVC projects.
5. Minor grammar issues reduce confidence (e.g., "want to it match", "layout file", past tense in bullet lists).
6. No updated sample demonstrating current LTS/STS.

Resolution Strategy

Create a single new .NET 9 sample and reuse its code for .NET 8:

• Folder: aspnetcore/security/authentication/add-user-data/samples/9.x/SampleApp
• TargetFramework: net9.0
• Snippets referenced by both .NET 9 and .NET 8 monikers; .NET 8 moniker adds a note that code is identical.

Rationale:

• Identity customization steps unchanged between 8 and 9.
• Minimizes duplication and maintenance.
• Improves credibility by presenting a "current" sample.

Documentation Changes (High-Level)

1. Metadata

   • Update ms.date to a current date (e.g., 10/15/2025).

2. Moniker Restructure

   • Add :::moniker range=">= aspnetcore-9.0" (primary instructions, points to 9.x sample).
   • Add :::moniker range=">= aspnetcore-8.0 < aspnetcore-9.0" referencing 9.x sample, noting identical code.
   • Adjust existing >= aspnetcore-6.0 to >= aspnetcore-6.0 < aspnetcore-8.0 for legacy.
   • Leave 3.x and <3.0 as-is (with grammar fixes).

3. New Sections / Enhancements

   • "Quick checklist" for adding two properties (FirstName, LastName).
   • Explicit project creation instructions for both Razor Pages ...