如何在ASP.NET MVC中实现角色？

<configuration>
  <system.web>
    <roleManager enabled="true" defaultProvider="AspNetSqlRoleProvider">
      <providers>
        <clear />
        <add name="AspNetSqlRoleProvider" type="System.Web.Security.SqlRoleProvider" connectionStringName="YourConnectionString" applicationName="YourAppName" />
      </providers>
    </roleManager>
  </system.web>
</configuration>

if (!Roles.RoleExists("Admin"))
{
    Roles.CreateRole("Admin");
}

if (!Roles.IsUserInRole("username", "Admin"))
{
    Roles.AddUserToRole("username", "Admin");
}

[Authorize(Roles = "Admin")]
public class AdminController : Controller
{
    // Actions for admin only
}