CODE EXAMPLE FOR CSHARP

custom attribute for auth permission check .net

public class MyAuthAttribute : Attribute, IAuthorizationFilter
{
    public void OnAuthorization(AuthorizationFilterContext context)
    {
        //check access 
        if (CheckPermissions())
        {
            //all good, add some code if you want. Or don't
        }
        else
        {
            //DENIED!
            //return "ChallengeResult" to redirect to login page (for example)
            context.Result = new ChallengeResult(CookieAuthenticationDefaults.AuthenticationScheme);
        }
    }
}
That's it. No need to mess with "policies", "claims", "handlers" and other [beep]

Usage:

// GET api/Get/5
[MyAuth]
public ActionResult<string> Get(int id)
{
    return "blahblah";
}