Using ResourcePopulationMode in ServerSide and Authentication

If you set ResourcePopulationMode="ServerSide" and use authentication as shown below:

<telerik:radscheduler runat="server" id="RadScheduler1">       
   <WebServiceSettings Path="../SchedulerWebService.asmx" ResourcePopulationMode="ServerSide" />
</telerik:radscheduler> 

<system.web>
   <authentication mode="Forms">
     <forms cookieless="UseCookies"
       loginUrl="~/login.aspx"/>
   </authentication>
   <authorization>
     <deny users="?"/>
     <allow users="*"/>
   </authorization>
</system.web>     

you may experience the following error (or similar):

The remote server returned an error: (401) Unauthorized.

The solution is to set the authentication cookie in ResourcesPopulating:

using System.Net;
using System.Web;
using System.Web.Security;
//
protected void RadScheduler1_ResourcesPopulating(object sender, Telerik.Web.UI.ResourcesPopulatingEventArgs e)
{
   HttpCookie cookie = FormsAuthentication.GetAuthCookie(User.Identity.Name, false);
   string cookieHeader = string.Format("{0}={1}", cookie.Name, cookie.Value);
   e.Headers.Add(HttpRequestHeader.Cookie, cookieHeader);
} 

Imports System.Web
Imports System.Net
Imports System.Web.Security
''
Protected Sub RadScheduler1_ResourcesPopulating(ByVal sender As Object, ByVal e As Telerik.Web.UI.ResourcesPopulatingEventArgs)
    Dim cookie As HttpCookie = FormsAuthentication.GetAuthCookie(User.Identity.Name, False)
    Dim cookieHeader As String = String.Format("{0}={1}", cookie.Name, cookie.Value)
    e.Headers.Add(HttpRequestHeader.Cookie, cookieHeader)
End Sub

Another scenario when the "401: Unauthorized" error may be seen is when "Windows authentication" is used and the ResourcePopulationMode="ServerSide". In this case you should declare the NetWork credentials in the ResourcesPopulating event as it is done below. This only other thing that have to be done is to turn the impersonation off of because of the Double Hop issue that may occur as is explained here:

void RadScheduler1_ResourcesPopulating(object sender, ResourcesPopulatingEventArgs e) 
{ 
    var a = new NetworkCredential(); 
    a.UserName = Page.User.Identity.Name; 
    a.Password = "******"; 
    e.Credentials = a; 
} 

Private Sub RadScheduler1_ResourcesPopulating(sender As Object, e As ResourcesPopulatingEventArgs)

    Dim a = New NetworkCredential()
    a.UserName = Page.User.Identity.Name
    a.Password = "******"
    e.Credentials = a
End Sub