ASP.NET MVC - 操作HTTP Post

When a form is posted back to the server, is it possible to manipulate, change, set the values contained in HTTP Post in the controller action? I would like to remove certain textbox values entered by the user so that these values always have to be re-entered (e.g. password fields). By default Html helpers extract initial values for HTML controls from the HTTP Post info.When a form is posted back to the server, is it