Why Does My ASP.NET WebMethod Return a '401 (Unauthorized)' Error When Called via jQuery AJAX?

ASP.NET Calling WebMethod with jQuery AJAX Returns "401 (Unauthorized)"

An issue has been encountered when attempting to call a WebMethod in an ASP.NET Webform using jQuery AJAX, resulting in a "401 (Unauthorized)" error message.

The WebMethod in question, GetClients, is defined as follows:

[WebMethod]<br>public static string GetClients(string searchTerm, int pageIndex)<br>{<pre class="brush:php;toolbar:false">// ...

}

This WebMethod is being invoked from jQuery AJAX as follows:

function GetClients(pageIndex) {<pre class="brush:php;toolbar:false">$.ajax({
    // ...

}

However, upon making the AJAX request, the following error occurs:

POST http://localhost:64365/ConsultaPedidos.aspx/GetClients <strong>401<br>  (Unauthorized)</strong>

Further investigation reveals that this error arose after implementing user authentication within the web application. The authentication configuration is defined as follows:

<system.web><pre class="brush:php;toolbar:false"><authentication mode="Forms">
    <forms loginurl="~/Account/Login" timeout="2880" defaulturl="/Dashboard"></forms>
</authentication>
<authorization>
    <deny users="?"></deny>
</authorization>

To resolve this issue, the following steps were taken:

1. Disable Automatic Redirection: In the ~/App_Start/RouteConfig.cs file, comment out or change the following line:

settings.AutoRedirectMode = RedirectMode.Permanent;

2. Update AJAX URL: If friendly URLs are enabled, update the jQuery AJAX URL to use ResolveUrl:

url: ',<br>

By implementing these changes, the "401 (Unauthorized)" error was eliminated, and the WebMethod could be successfully called using jQuery AJAX.

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