Facebook Authentication with the Facebook C# SDK and ASP.NET MVC 4

AccountController.FacebookCallback1.cs

public ActionResult FacebookCallback(string code)
{
    var fb = new FacebookClient();
    dynamic result = fb.Post("oauth/access_token", new
    {
        client_id = "your_app_id_here",
        client_secret = "your_app_secret_here",
        redirect_uri = RedirectUri.AbsoluteUri,
        code = code
    });

    var accessToken = result.access_token;
            
    // TODO: Authenticate User
}

AccountController.FacebookCallback2.cs

public ActionResult FacebookCallback(string code)
{
    var fb = new FacebookClient();
    dynamic result = fb.Post("oauth/access_token", new
    {
        client_id = "444977858884680",
        client_secret = "0e82b0d234a172df378b10929a65fef1",
        redirect_uri = RedirectUri.AbsoluteUri,
        code = code
    });

    var accessToken = result.access_token;

    // Store the access token in the session
    Session["AccessToken"] = accessToken;

    // update the facebook client with the access token so 
    // we can make requests on behalf of the user
    fb.AccessToken = accessToken;

    // Get the user's information
    dynamic me = fb.Get("me?fields=first_name,last_name,id,email");
    string email = me.email;

    // Set the auth cookie
    FormsAuthentication.SetAuthCookie(email, false);

    return RedirectToAction("Index", "Home");
}

AccountController.Login.cs

public ActionResult Login()
{
    return View();
}

AccountController1.cs

public class AccountController : Controller
{
    //
    // GET: /Auth/

    public ActionResult Facebook()
    {
        throw new NotImplementedException();
    }
}

AccountController2.cs

public class AccountController : Controller
{
    private Uri RedirectUri
    {
        get
        {
            var uriBuilder = new UriBuilder(Request.Url);
            uriBuilder.Query = null;
            uriBuilder.Fragment = null;
            uriBuilder.Path = Url.Action("FacebookCallback");
            return uriBuilder.Uri;
        }
    }

    public ActionResult Facebook()
    {
        var fb = new FacebookClient();
        var loginUrl = fb.GetLoginUrl(new {
            client_id = "your_app_id_here",
            redirect_uri = RedirectUri.AbsoluteUri,
            response_type = "code",
            scope = "email" // Add other permissions as needed
        });

        return Redirect(loginUrl.AbsoluteUri);
    }

}

HomeController.cs

[Authorize]
public class HomeController : Controller
{
    //
    // GET: /Home/

    public ActionResult Index()
    {
        return View();
    }

}

Login.cs.html

@{
    ViewBag.Title = "Login";
}

<h2>Login</h2>
@Html.ActionLink("Login with Facebook", "Facebook")