Managing external user IDs becomes crucial as businesses provide more digital services to clients, partners, and outside developers. By offering a standards-based, scalable, and safe identification solution that works well with contemporary apps, Microsoft Entra External ID assists in overcoming this difficulty. 

 This article will demonstrate how to combine an ASP.NET Core MVC application with Microsoft Entra External ID. Setting up authentication, managing user claims, and enforcing authorization for external users will all be covered. This article will assist you in implementing identity management, whether you're creating a secure, user-friendly application or a multi-tenant SaaS platform.

Get started with Integration
Step 1. Open Visual Studio 2022, click on Create a New Project, select ASP.NET Core Web App (MVC) Template, provide a project name, and click Next to get a wizard below.

Step 2. In the service dependencies wizard, add the dotnet misidentify tool to add a Microsoft identity platform, and click Next

Step 3. Select the tenant and click Create New to register a new External Entra ID application or select an existing application,  as shown in the figure below.

Step 4. The next step is to add Microsoft Graph or any other API. For a demo, I'm just going to skip this process.
Finally, click next; it will scaffold all required NuGet packages and changes in the Program.cs, appsettings.json

Step 5. In this step, switch to entra.microsoft.com and ensure you are in the External ID tenant, go to the user flow. Please refer to my article to check how to create a user flow. Select the user flow and click on Application to link our application to the user flow, as shown in the figures below.

Step 6. Finally, run the application. It will display the Microsoft Entra External ID user flow sign-in screen. Sign in using your social account credentials. After successful authentication, the application will navigate to the Home screen.

Summary
A detailed tutorial on how to integrate Microsoft Entra External ID with an ASP.NET Core MVC application has been shown to us. It clarifies key ideas including maintaining user claims, implementing secure access controls, and configuring authentication for external users. Developers may improve application security and offer a smooth experience for external partners, clients, and vendors by leveraging Microsoft's identity platform. The manual supports identity management's strategic strategy as well as its technical implementation.