Introduction: Integrating Facebook authentication into your .NET project offers a user-friendly login option, allowing users to sign in with their Facebook credentials. This guide will walk you through the steps to implement Facebook login, enhancing user convenience, trust, and providing access to user data. Creating a Demo for Facebook Authentication in .NET Step 1: Set Up .NET Project  1. Create a new ASP.NET MVC project using Visual Studio or your preferred IDE.  Step 2: Create Facebook Developer App  2. Go to the [Facebook Developer Portal] : https://developers.facebook.com/ 3. Create a new app.  4. Configure the app details and obtain the App ID and App Secret.     Step 3: Configure Facebook Authentication in .NET Project  5. In your .NET project, open `Startup.cs`.  6. Configure Facebook authentication:  services.AddAuthentication(options =>     {         options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;         options.DefaultChallengeScheme = FacebookDefaults.AuthenticationScheme;     })    .AddCookie()     .AddFacebook(options =>     {         options.AppId = "Your-Facebook-App-ID";         options.AppSecret = "Your-Facebook-App-Secret";         options.CallbackPath = new PathString("/Auth/FacebookCallback");    });  Step 4: Create AuthController  7. Create an `AuthController` with actions for Facebook login and callback:  public class AuthController : Controller     {         public IActionResult Index()         {             return View();         }         [HttpGet]         [Route("signin-facebook")]         public async Task<IActionResult> FacebookCallback()         {             var result = await HttpContext.AuthenticateAsync("Facebook");             if (result.Succeeded)             {                 // Authentication succeeded. Add your logic here.                 return RedirectToAction("Index", "Home");             }             // Authentication failed. Handle the error.             return RedirectToAction("Login", "Account");         }         public IActionResult FacebookLogin()         {             var properties = new AuthenticationProperties             {                 RedirectUri = Url.Action("https://localhost:7135/Auth/FacebookCallback"),             };              return Challenge(properties, FacebookDefaults.AuthenticationScheme);         }     }  Step 5: Implement Facebook Login Button  8. In your `Index.cshtml` or another appropriate view, add a button for Facebook login: <h1>Facebook Authentication</h1>  <button class="btn btn-primary"><a style="color:white" asp-controller="Auth" asp-action="FacebookLogin">Login with Facebook</a></button>  Step 6: Update App Settings  9. In the Facebook Developer Portal, update the "Valid OAuth Redirect URIs" with `https://localhost:7135/Auth/FacebookCallback`.    Login Facebook > Settings. Step 7: Run and Test  10. Run your .NET project and test the Facebook authentication by clicking the "Login with Facebook" button.      Click on Login with Facebook > Continue. You can create Successful login in redirect logic. You Can also use JavaScript SDK to use authenticate in Your project I n our case will use MVC    Here will use the same app we already create just we will Update the controller action to JS function provided by "Meta Developer" Quick Start Add this JavaScript code in your view where your login button is available  <button class="btn btn-primary"><a style="color:white" onclick="loginWithFacebook()">Login with Facebook</button> <script> window.fbAsyncInit = function () { FB.init({ appId: '1438230313570431', xfbml: true, version: 'v19.0' }); FB.AppEvents.logPageView(); }; (function (d, s, id) { var js, fjs = d.getElementsByTagName(s)[0]; if (d.getElementById(id)) { return; } js = d.createElement(s); js.id = id; js.src = "https://connect.facebook.net/en_US/sdk.js"; fjs.parentNode.insertBefore(js, fjs); }(document, 'script', 'facebook-jssdk')); function loginWithFacebook() { FB.login(function (response) { if (response.authResponse) { // User is logged in and authorized your app console.log('Successful login for: ' + response.authResponse.userID); console.log(response); debugger; window.location = "https://localhost:44304/Auth/SuccesfullLogin"; } else { // User cancelled login or did not authorize your app console.log('Login cancelled'); } }, { scope: 'public_profile,email' }); // Specify the required permissions } </script> Now we Have to add js.src link in your JS functions is need to be Added in Meta developer App In our case it is :   https://connect.facebook.net/en_US/sdk.js will go to again Use cases > customize > settings.  Will add our link in "Allowed Domains for the JavaScript SDK" section Make sure "Login with the JavaScript SDK" toggle is "Yes". Now, you have a comprehensive guide for creating a demo on Facebook authentication in a .NET project. Share this guide, and users can follow each step to implement Facebook login functionality in their ASP.NET applications.