How to use Roles in ASP.NET Core 2.1?

In addition to the answers already provided, despite adding .AddRoles<Identity>(), I still could not get Authorization when use Authorize(Roles = "Administrator") on my controllers. For some reason,the "role claim doesn't seem to affect IsUserInRole or AuthorizeAttribute with a role name."

To make use of roles I would suggest that one use the ASP.NET 2.0 way like below:

services.AddIdentity<IdentityUser, IdentityRole>()
            .AddDefaultUI()
            .AddDefaultTokenProviders()
            .AddEntityFrameworkStores<ApplicationDbContext>();

This way, you get to use your roles and also get the Identity pages scaffolded for you.

Refer to this issue on aspnet github: Issue 1813

It seems that finally Microsoft understood that not every application needs roles and separated them.

Notice that AddDefaultIdentity is declared as:

public static IdentityBuilder AddDefaultIdentity<TUser>(this IServiceCollection services) where TUser : class;

So, you can continue to configure Identity options through that IdentityBuilder. What you want to do is:

services.AddDefaultIdentity<IdentityUser>().AddRoles<IdentityRole>();

Fortunately, they also removed the IUser and IRole constrains, so now you can use models in a completely separate assembly without having to install hundreds of NuGet packages.

Might help someone else: If you add asp.net identity through scaffolding to an existing project, you'll need to edit the IdentityHostingStartup.cs and change the services there instead of in your startup class:

services.AddIdentity<AppUser, IdentityRole>()
                .AddDefaultUI()
                .AddRoles<IdentityRole>()
                .AddRoleManager<RoleManager<IdentityRole>>()
                .AddDefaultTokenProviders()
                .AddEntityFrameworkStores<authContext>();

And then you can use the role manager in your seeding.