why logged in user redirected to login page

1. Restricting Access for Logged-in Users:

The [Authorize] attribute and User.IsInRole serve different purposes:

• [Authorize]: This attribute is ideal for declarative authorization. You can specify roles or policies directly on controllers or actions. If a user doesn't have the required permissions, they'll be redirected to a login page (by default) or receive an unauthorized response (API).
• User.IsInRole: This method provides a programmatic way to check a user's roles within your code. You can use it to conditionally render UI elements, handle business logic, or redirect users dynamically based on roles.

Here's how to combine them effectively:

• Use [Authorize] to declare overall access restrictions for controllers or actions.
• Inside your controller methods, use User.IsInRole to perform additional role-based checks or customizations for the logged-in user.

This avoids unnecessary login prompts when the user is already authenticated but doesn't have the necessary permissions according to the [Authorize] attribute.

2. Multi-User Application with Restricted Pages:

To achieve this scenario:

• Implement a mechanism to identify restricted users. This could be based on roles, user data, or a custom flag in your user model.
• Use [Authorize] on the restricted pages to enforce access control.
• Instead of redirecting to a login page for unauthorized users, redirect them to a designated "access denied" or "forbidden" page within your application. This avoids showing the login page again.

Here is an example code: -

// User model (example)
public class User
{
    public bool IsRestricted { get; set; }
    // Other user properties
}

// Controller action with authorization and role check
[Authorize]
public IActionResult MyAction()
{
    if (User.IsInRole("Admin") || !User.IsRestricted)
    {
        // Allow access for admins and non-restricted users
        return View();
    }
    else
    {
        return RedirectToAction("AccessDenied"); // Redirect to a custom error page
    }
}

// Access denied page
public IActionResult AccessDenied()
{
    return View();
}

In the above source code, restricted users attempting to access MyAction will be redirected to the AccessDenied view instead of the login page. Remeber to Configure your user authentication system to store and retrieve user roles or restricted flags efficiently. Design a clear and informative "Access Denied" page to guide users who lack the necessary permissions.

By combining [Authorize] and User.IsInRole, you can create a more granular and user-friendly authorization system in your ASP.NET Core application