Role based authorization not working in .net 5

If you have a custom User that inherits from IdentityUser

For example:

public class ApplicationUser : IdentityUser
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

And you have your services configured properly, like so:

services.AddDefaultIdentity<ApplicationUser>(options => options.SignIn.RequireConfirmedAccount = true)
                    .AddRoles<IdentityRole>()
                    .AddRoleManager<RoleManager<IdentityRole>>() /* Added role manager*/
                    .AddDefaultUI()
                    .AddEntityFrameworkStores<ApplicationDbContext>();

That should work fine if you are not using a custom claim principal for UserPrincipal.

For example:

public class AppUserClaimsIdentityFactory : UserClaimsPrincipalFactory<ApplicationUser>
{   
    public AppUserClaimsIdentityFactory(
            UserManager<ApplicationUser> userManager,
            IOptions<IdentityOptions> optionsAccessor)
            : base(userManager, optionsAccessor)
    {
    }
    
    /* code implementation */
}

and injected it using DI like below:

services.AddScoped<IUserClaimsPrincipalFactory<ApplicationUser>, AppUserClaimsIdentityFactory>();

In that case it doesn't work, you'll need to use a different constructor overload for UserClaimsPrincipalFactory and add role manager to it.

Update your custom UserClaimsIdentityFactory:

public class AppUserClaimsIdentityFactory : 
        UserClaimsPrincipalFactory<ApplicationUser,
                                   IdentityRole>
        /* Note: you can use your custom Role class or identity default */
{
    public AppUserClaimsIdentityFactory(
            UserManager<ApplicationUser> userManager,
            RoleManager<IdentityRole> roleManager, /* Add role manager */
            IOptions<IdentityOptions> optionsAccessor)
            : base(userManager, roleManager /* send it to base constructor */, optionsAccessor)
    {
    }

    /* code implementation */
}

You don't have to change anything in Dependency Injection container for your custom UserClaimsPrincipalFactory.

Everything thing should work fine as expected.