How to Automatically Authenticate a User Against All Trusted Domains in ISA

When you use Basic authentication in Internet Security and Acceleration (ISA) Server to authenticate Web Proxy users, ISA does not automatically try to authenticate the user against all trusted domains when no domain name is specified by the user. This occurs even if a backslash (\) is specified as the default authentication domain under Basic authentication for the Web Proxy listener in question.

When you use Basic authentication to authenticate Web Proxy users, if the user only specifies "username" instead of "domainname\username" when the user is prompted for credentials in the browser, ISA only tries to authenticate the user against the default authentication domain that is specified under Basic authentication for the Web Proxy listener. If no default authentication domain is specified, ISA only tries to authenticate the user against the domain that the ISA server itself is a member of.

Although this is by design in ISA Server, a code update has been produced to help alleviate this issue because customer feedback indicates that this is an important feature.

You must install ISA Server Service Pack 1 (SP1) before you apply the following hotfix.

For additional information about how to obtain the latest ISA Server service pack, click the article number below to view the article in the Microsoft Knowledge Base: A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language. To install the fix, run the self-extracting file. You do not have to restart the ISA Server computer. If the computer is part of an ISA Server array, you do not have to shut the whole array down; you can still install this fix on a one-by-one basis.

The English version of this fix should have the following file attributes or later:
This fix also applies to the French, German, Spanish, and Japanese versions of ISA Server.

If the user specifies "domainname\username" instead of only "username" when the user is prompted for credentials in the browser, the user is immediately authenticated against the correct domain where the user account exists. Also, if the user accounts exists in the domain where the ISA server itself is member, the "username" syntax is enough to authenticate the user.

The new feature in this hotfix is only useful when you use Basic authentication, when the user is not familiar with the "domainname\username" syntax, and when the user account exists in a domain that is different from the domain where the ISA server itself is a member.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

To implement the functionality in this fix and then enable it, follow these steps after you have installed the fix:

1. Stop the Web Proxy service.
2. Start Registry Editor.
3. Locate and then click the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W3Proxy\Parameters
4. Create a new DWORD value named TreatSlashBasicDomainAsAllTrustedDomains. Give this new value a data value of 1.
5. On the required Web Proxy listener (either on the Outgoing Web Requests tab, the Incoming Web Requests tab, or both depending on where this feature is needed), specify a backslash (\) as the default authentication domain for Basic authentication.
6. Start the Web Proxy service.

To revert to the original configuration, either remove the TreatSlashBasicDomainAsAllTrustedDomains registry value, or change its data value to 0 (zero). Also, remove the backslash (\) from the default authentication domain and either clear the Default Authentication Domain text box or change the value to the required domain. After you make both of these changes, restart the Web Proxy service.

Note that this feature causes ISA to try to authenticate the user against all trusted domains until a match is found or until the search for the user is completed without finding the matching account name. Depending on the number of trusted domains, this may have a small performance impact.