In AutoCompleteExtender how can I get/access the response on client side in order to redirect the page?

Question

Is there a way that AutoCompleteExtender of AjaxControlToolkit provide to access its response similar to ajax success function callback. Actually I am authenticating a call to webmethod. If a request is not authentic I am returning "500" from my webmethod, but if it is authentic request it should work verbatim.

Below is the markup of my AutoCompleteExtender

<ajx:AutoCompleteExtender ID="AutoCompleteExtender1" runat="server"
    TargetControlID="txtsearch" 
    ServicePath="SearchWebService.asmx" 
    ServiceMethod="GetWorsList" 
    MinimumPrefixLength="1" 
    CompletionSetCount="20" 
    CompletionInterval="0" 
    EnableCaching="true" 
    CompletionListElementID="autocompleteList" >
</ajx:AutoCompleteExtender>

Below is the code behind

[WebMethod]
public object GetWorsList(string prefixText)
{
    List<string> workNames = null;
    if (ConfigurationManager.AppSettings["Header-Name"].ToString() !=
        HttpContext.Current.Request.UrlReferrer.Host.ToString())
    {        
        return "500";        
    }
    else
    {
        /*Success Part*/
    }    
}

I want to access the "500" value on my client side so that I can redirect to Logout.aspx page.

I tried OnClientPopulated as per link 1 and link 2, but I am getting Parser Error Message: Type 'AjaxControlToolkit.AutoCompleteExtender' does not have a public property named 'OnClientPopulated'.

Which left me no other option to ask question here.

EDIT:

The JS I tried is below:

<script type="text/javascript">
 function ResponseRedirecttoLogout(sender, args)
 {
            
    if (args.get_response() === "500") {
               
      window.location.href = 'logout.aspx';
    }
 }
</script>