app.MapPost("/widget", (CreateWidgetDTO dto) =>
{
    // Use the dto
});

public abstract class DTO<T>
{
    // typeof(T) must equal ParameterInfo.Type otherwise we throw
    public static T BindAsync(HttpContext context, ParameterInfo parameter)
    {
        // Use reflection to bind the properties on T
    }
}

public class CreateWidgetDTO : DTO<CreateWidgetDTO>
{
    [FromRoute]
    public string? Name { get; set; }

    [FromQuery]
    public int Id { get; set; }
}