Request.ServerVariables("LOGON_USER") returns empty string in ASP.NET

This article provides resolutions for the problem where the Request.ServerVariables("LOGON_USER") variable returns empty string in ASP.NET.

Original product version:   ASP.NET
Original KB number:   306359

Symptoms

If you try to access the Request.ServerVariables("LOGON_USER") variable in ASP.NET, an empty string is returned.

If you are using Microsoft Visual C# .NET, the following syntax accesses this variable:

Request.ServerVariables["LOGON_USER"]

Cause

This problem occurs because the authentication-related variables in the ServerVariables collection are not populated if you use Anonymous Access security to access the .aspx page. This problem can also occur if you give the anonymous user access in the <authorization> section of the web.config file.

Resolution

To populate the LOGON_USER variable when you use any authentication mode other than None, you can deny access to the anonymous user in the <authorization> section of the web.config file. To deny access to the anonymous user in the <authorization> section, follow these steps:

  1. Change the authentication mode in the web.config file to anything other than None. For example, the following entry in the web.config file sets the authentication mode to Forms-based authentication:

    <authentication mode="Forms" />
    
  2. To deny access to the anonymous user in the web.config file, use the following syntax:

    <authorization>
        <deny users = "?" /> <!-- This denies access to the anonymous user -->
        <allow users ="*" /> <!-- This allows access to all users -->
    </authorization>
    

If you are using Windows authentication, you can also use the following steps to resolve this problem:

  1. Change the authentication mode in the web.config file to Windows as follows:

    <authentication mode="Windows" />
    
  2. In the Internet Services Manager, right-click the .aspx file or the Web Project folder, and then select Properties.

  3. If you select Properties for the Web Project folder, select the Directory Security tab. If you select Properties for the .aspx file, select the File Security tab.

  4. Under Anonymous Access and authentication control, select Edit.

  5. In the Authentication methods dialog box, clear the Anonymous Access check box, and then select the Basic, the Digest, or the Integrated (NT Challenge/Response) check box.

  6. Select OK to close both dialog boxes.

Status

This behavior is by design.

More information

ASP.NET provides new authentication modes and authorization schemes, which you can configure in the .config files. For this reason, modifying the authentication modes in IIS alone may not always yield the desired results. Therefore, you must also consider the security settings in the .config files.

Note

When you enable Anonymous authentication in conjunction with Windows authentication or if you grant access to the anonymous user in the <authorization> section while you are using any authentication mode other than None, other server variables such as AUTH_USER and REMOTE_USER (as well as the HttpContext.Current.User.Identity.Name property) also return an empty string. You can use the any of the above-mentioned resolutions to populate these variables.

In ASP.NET, you can also use the IsAuthenticated property of the Request object to determine whether the Anonymous Access security is being used. IsAuthenticated returns false if Anonymous Access is turned on and returns true if you use any other means of authentication such as Forms, Passport, Integrated (NT Challenge/Response), or Basic.

References