Q:

Apply Authorize filter on all controllers within an area

How can I force authorization on all controllers within an area? Specifically, I would like to configure an AuthorizeFilter to be applied on the 'admin' area as part of the Startup.ConfigureServices() method.

A:

One way do to this is with the use of a custom IControllerModelConvention
public class AuthorizeAreaConvention : IControllerModelConvention
{
    private readonly string _area;
    private readonly string _policy;

    public AuthorizeAreaConvention(string area, string policy)
    {
        _area = area;
        _policy = policy;
    }

    public void Apply(ControllerModel controller)
    {
        if (controller.Attributes.Any(a => 
                a is AreaAttribute && (a as AreaAttribute).RouteValue.Equals(_area, StringComparison.OrdinalIgnoreCase))
            || controller.RouteValues.Any(r =>
                r.Key.Equals("area", StringComparison.OrdinalIgnoreCase) && r.Value.Equals(_area, StringComparison.OrdinalIgnoreCase)))
        {
            controller.Filters.Add(new AuthorizeFilter(_policy));
        }
    }
}

Then in your Startup.ConfigureServices() method, you can add:
services.AddMvc(options =>
{
    options.Conventions.Add(
            new AuthorizeAreaConvention("Admin", Policy.AdministratorPolicy));
});

Where Policy.AdministratorPolicy is just a string constant (e.g. "AdministratorPolicy") which is registered in the app StartUp as follows:
public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthorization(o =>
    {
        o.AddPolicy(Policy.AdministratorPolicy, b =>
        {
            b.RequireAuthenticatedUser();
            b.RequireClaim(ClaimTypes.Role, Roles.Admin);
        });
    });

    // Add framework services.
    services.AddMvc();
    // ... Omitted for brevity
}

In the above, Roles.Admin is just a string constant (e.g. "Admin").

