ASP.Net Web Application Request.Params["AUTH_USER"] is empty string - asp.net

Question

I'm building an ASP.Net 4.5 Web Application in Visual Studio 2012. I've put the following code in my Global.asax.cs:
protected void Session_Start(object sender, EventArgs e)
{
Session["LastError"] = "";
// Code that runs when a new session is started
string delimStr = #"\";
char[] delimiter = delimStr.ToCharArray();
string[] requestor = Request.Params["AUTH_USER"].ToString().Split(delimiter, 2);
string requestorEID = requestor[1];
Session["UserID"] = requestorEID;
//Get User data (name, roleid, rolename) from database
List<SqlParameter> paramList = new List<SqlParameter>();
paramList.Add(new SqlParameter("#EmployeeID", requestorEID));
DataTable dtUserList = KLClassLibrary.KLDataAccessLayer.ExecuteSelect("GetUserData", paramList, "OffSiteCN");
if (dtUserList.Rows.Count > 0)
{
Session["EmployeeName"] = dtUserList.Rows[0]["EmployeeName"].ToString();
}
else
{
Session["LastError"] = "You Are Not Authorized To Access This Application";
Session["EmployeeName"] = "";
Response.Redirect("~/ErrorPage.aspx");
}
}
Whenever my code gets to the line
string[] requestor = Request.Params["AUTH_USER"].ToString().Split(delimiter, 2);
Request.Params["AUTH_USER"] is equal to an empty string. I've used this code successfully for years, although I'm new to VS2012 and .Net 4.5. What's wrong?

Answer 1

This isn't a complete solution, but I was able to create a workaround by using the following code:
string requestor = Request.LogonUserIdentity.Name.ToString();
int requestor_length = requestor.Length;
string requestorEID = requestor.Substring(requestor_length - 5, 5);
Session["UserID"] = requestorEID;

Answer 2

Ensure you have "Windows Authentication" enabled in the project's properties (it is the very bottom of the properties list). This will allow IISExpress to use windows authentication.
Then ensure you have denied access to anonymous users in your web.config's system.web authorization section, system.webServer or both.
For IIS 6.5 or below:
<system.web>
<authorization>
<deny users="?"/>
</authorization>
</system.web>
For IIS 7 or above
<system.webServer>
<security>
<authorization>
<add accessType="Deny" users="?"/>
</authorization>
</security>
</system.webServer>
you can also set the windows authentication modes in these sections, but the server must allow you to override their default setting. IISExpress is not set to allow this value to be overridden so you can not try to set it here for your debug mode.
The older versions of Visual Studio used Cassini to emulate a web server for your debugging. Now it uses IISExpress, which will deliver you a closer experience to a true IIS server. There used to be certain scenarios that would differ between Cassini and your actual IIS server - now it is rare to non-existent that I run into these issue. However with correct configuration settings you can get your AUTH_USER value on session start.