Well beside the answers, I just found the answer which is totally predefined in asp .net core. When you are adding claims just :
var claims = new List<Claim>
{
new Claim(ClaimTypes.Name, UserName),
new Claim(ClaimTypes.Role, "User"),
new Claim(ClaimTypes.Role, "Admin"),
new Claim(ClaimTypes.Role, Watever)
};
after that you can just use it as said:
[Authorize(Roles = "Watever")]
or
User.IsInRole("Watever")