Why Am I Getting a 401 Unauthorized Error When Calling an ASP.NET WebMethod with jQuery AJAX?

Unauthorized WebMethod Call with ASP.NET and jQuery AJAX

Issue Description

Users face authorization errors (401) when attempting to call a WebMethod in ASP.NET using jQuery AJAX. The error message typically reads as "Authentication failed."

Background

The WebMethod is declared in a WebForm as:

[WebMethod]
public static string GetClients(string searchTerm, int pageIndex) { /*...*/ }

However, upon calling the WebMethod with:

$.ajax({ /*...*/
    url: "ConsultaPedidos.aspx/GetClients",
    /*...*/
});

the browser responds with a 401 Unauthorized error.

Solution

The solution to this issue involves disabling the automatic redirection mechanism in ASP.NET:

1. Navigate to ~/App_Start/RouteConfig.cs.

2. Locate the line:

   settings.AutoRedirectMode = RedirectMode.Permanent;

3. Change it to:

   settings.AutoRedirectMode = RedirectMode.Off;

   Alternatively, you can comment out the line.

Additional Modification:

If friendly URLs are enabled in the application, you must also change:

url: "ConsultaPedidos.aspx/GetClients",

to:

url: '<%= ResolveUrl("ConsultaPedidos.aspx/GetClients") %>',

Explanation:

By default, ASP.NET automatically redirects unauthorized requests to the login page. Disabling this behavior allows the WebMethod call to proceed.

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