Asp.net mvc 5 从mvc5中的控制器发布到外部表单

我在mvc5视图中有一个带有按钮的表单。我需要在控制器中处理这个表单，并添加几个字段值，这些值从控制器中获取，然后发布到外部url

@using (Html.BeginForm()) 
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h4>Deal</h4>
        <hr />
        @Html.ValidationSummary(true)

        <div class="form-group">
            @Html.LabelFor(model => model.First_Name, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.TextBoxFor(model => model.First_Name, new { @class = "form-control" })
                @Html.ValidationMessageFor(model => model.First_Name)
            </div>
        </div>
        <div class="form-group">
            @Html.LabelFor(model => model.Last_Name, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.TextBoxFor(model => model.Last_Name, new { @class = "form-control" })
                @Html.ValidationMessageFor(model => model.Last_Name)
            </div>
        </div>
<div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Save" class="btn btn-default" name="save" /> 
                <input type="submit" value="Register Deal" class="btn btn-default" name="submit" />
            </div>

        </div>

我们如何才能做到这一点，有什么想法吗

一个用例是

---

如果向用户提供用户名，那么我需要从数据库中查询姓氏、年龄等信息，并将其提交到另一个网站的注册表中，您可以使用Web请求方法发布。例如

public void post()
{
    string URL = "http://";
    System.Net.WebRequest webRequest = System.Net.WebRequest.Create(URL);
    webRequest.Method = "POST";
    webRequest.ContentType = "application/x-www-form-urlencoded";
    Stream reqStream = webRequest.GetRequestStream();
    string postData = Request.QueryString; //you form data in get format 
    byte[] postArray = Encoding.ASCII.GetBytes(postData);
    reqStream.Write(postArray, 0, postArray.Length);
    reqStream.Close();
    StreamReader sr = new StreamReader(webRequest.GetResponse().GetResponseStream());
    string Result = sr.ReadToEnd();
}

---

字符串postData=Request.QueryString//以get格式形成数据。我该怎么做？你的控制器中有Request.QueryString，只需获取它并附加额外的字段hanks..你能给我一个附加额外字段的小例子吗。我在请求时确实收到错误。querystring无法将类型“System.Collections.Specialized.NameValueCollection”隐式转换为“string”，这样可以工作吗

public void post()
{
    string URL = "http://";
    System.Net.WebRequest webRequest = System.Net.WebRequest.Create(URL);
    webRequest.Method = "POST";
    webRequest.ContentType = "application/x-www-form-urlencoded";
    Stream reqStream = webRequest.GetRequestStream();
    string postData = Request.QueryString; //you form data in get format 
    byte[] postArray = Encoding.ASCII.GetBytes(postData);
    reqStream.Write(postArray, 0, postArray.Length);
    reqStream.Close();
    StreamReader sr = new StreamReader(webRequest.GetResponse().GetResponseStream());
    string Result = sr.ReadToEnd();
}