How to use inheritance in controller action request?

Question

What is the easiest way to use inheritance in action using ASP.NET CORE MVC?

For example, I have 3 classes:

public class Common
{
  public string CommonField { get; set; }
}

public class A : Common
{      
  public string FieldA { get; set; }
}

public class B : Common
{
  public string FieldB { get; set; }
}

I have controller action

IActionResult Post([FromBody] [ModelBinder(BinderType = typeof(MyCustomeBinder))] Common field)
{
  //process field here
}

what is the best way to replace field initialization(based on some query parameter (for example, type=a)) in action before binding? I still need all properties to be filled from body.

I already have something like:

public class MyCustomBinder : IModelBinder
{
  public Task BindModelAsync(ModelBindingContext bindingContext)
  {
    switch (bindingContext.HttpContext.Request.Headers["type"])
            {
                case "a":
                    bindingContext.Result = ModelBindingResult.Success(new A());
                    break;
                case "b":
                    bindingContext.Result = ModelBindingResult.Success(new B());
                    break;
                default:
            }

                return TaskCache.CompletedTask;
  }
}

It's correct object coming to action, but all fields are empty.