修改ActionFilterAttribute中的HTTP内容

Question

我将控制器操作设置为：

[HttpPost]
[DecryptBodyFilterAttribute]
public InitializeSessionResponse InitializeSession([FromBody] InitializeSessionRequest request)
{
  ...
}

http主体是json并自动被反序列化到我的请求对象中就好了。现在我想让http正文内容成为加密字符串，我将在ActionFilterAtttribute中解密。加密/解密不是问题。我的问题是在进入控制器中的操作之前将body的值重置为新值。

我的ActionFilterAttribute如下所示：

 public sealed class DecryptBodyFilterAttribute : ActionFilterAttribute
 {
    public DecryptBodyFilterAttribute()
    {}

    public override Task OnActionExecutingAsync(HttpActionContext actionContext, System.Threading.CancellationToken cancellationToken)
    {
        string encryptedString = actionContext.Request.Content.ReadAsStringAsync().Result;
        //... decrypt do whatever and end up with the new content below...

        string newContent = "Something here would be the decrypted json of the initializeSessionRequest";
        //I need to do something like the below
        //actionContext.Request.Content = newContent;

        return base.OnActionExecutingAsync(actionContext, cancellationToken);
    }
 }

我的问题类似于Modify HttpContent (actionExecutedContext.Response.Content) in OnActionExecuted method of WebApi's ActionFilterAttribute，但是在转换response.content（在我的情况下请求中）时，我得到一个null对象，因此对我来说不起作用。