how to get URL result from a an action result of URL redirection

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C#

Greeting All ,
I want to get the result of an URL redirection from my ActionResult .
I have a first URL that I should redirect , how can I get the resulted URL
this is my code :

public ActionResult Auth()
{
    string loginUrl = "https://www.linkedin.com/uas/oauth2/authorization?" +
             "response_type=code" +
             "&client_id=" + API
             + "&state=DCEEFWF48883sdffef424"
             + "&redirect_uri=" + redirect_uri ;
    Redirect(loginUrl);
    //string codeParameter = HttpUtility.ParseQueryString(loginUrl).Get("client_id");
    //string url = System.Web.HttpContext.Current.Request.Url.AbsoluteUri;
    return Redirect(loginUrl);

}

Thanks in advance .