CODE EXAMPLE FOR CSHARP

custom attribute for auth permission check .net

public class Over18Requirement : AuthorizationHandler<Over18Requirement>, IAuthorizationRequirement
{
  public override void Handle(AuthorizationHandlerContext context, Over18Requirement requirement)
  {
    if (!context.User.HasClaim(c => c.Type == ClaimTypes.DateOfBirth))
    {
      context.Fail();
      return;
    }

    var dobVal = context.User.FindFirst(c => c.Type == ClaimTypes.DateOfBirth).Value;
    var dateOfBirth = Convert.ToDateTime(dobVal);
    int age = DateTime.Today.Year - dateOfBirth.Year;
    if (dateOfBirth > DateTime.Today.AddYears(-age))
    {
      age--;
    }

    if (age >= 18)
    {
      context.Succeed(requirement);
    }
    else
    {
      context.Fail();
    }
  }
}


//Then in your ConfigureServices() function you'd wire it up

services.AddAuthorization(options =>
{
    options.AddPolicy("Over18", 
        policy => policy.Requirements.Add(new Authorization.Over18Requirement()));
});

//And finally, apply it to a controller or action method with

[Authorize(Policy = "Over18")]