IIS Samples - ISAPI AuthFilt

AuthFilt demonstrates how to write an authentication filter based on an external datasource. Authentication is the process of accepting or denying a request from a client, so AuthFilt will be notified each time an authentication request comes in.

Warning   If you install this ISAPI filter on your server, make sure that you have configured IIS to restrict access to the virtual directory that contains the filter and the files you want to transmit. Also, set proper access control on the files in their physical folder. For more information, click Start, Help and Support, and search for Access Control.

Important   These samples are provided for educational purposes only. They are not intended to be used in a production environment, have not been tested in a production environment, and Microsoft does not provide technical support for them.

 

Sample Overview
Requirements
Location of the Source Code
Build and Install the Sample
Run the Sample
Sample Output
Helpdesk

 

Sample Overview

This sample uses a file (c:\inetsrv\userdb.txt) to keep track of authorized users, but it might be modified to access a database which holds user info. The file c:\inetsrv\userdb.txt does not exist. Please look at Db.c to see how to construct such a file and change the location of the file if you so desire.

For each authentication request, AuthFilt first looks in a cache of recently authenticated users, and when that fails, AuthFilt looks in the userdb.txt file. This shows an efficient way to authorize connections: a cache allows the filter to quickly authenticate users, and because each request comes in through the filter, speed is critical.

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Requirements

This sample requires the installation of the following software to function properly:

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Location of the Source Code

IIS samples are included in the IIS Software Developer Kit (SDK). You can download the IIS SDK from Platform SDK Update. You can view the SDK at MSDN Online. In the table of contents at MSDN Online, click Web Development, Server Technologies, Internet Information Services (IIS), SDK Documentation, Internet Information Services, Samples.

The following source code files are required for this sample:

File Description
AuthFilt.sln AuthFilt Visual Studio .NET solution file, required to build this sample in Visual Studio .NET.
AuthFilt.vcproj AuthFilt Visual Studio .NET C Project file, required to build this sample in Visual Studio .NET.
AuthFilt.dsp, AuthFilt.dsw AuthFilt Visual Studio Version 6 project files, required to build this sample in Visual Studio Version 6.
AuthFilt.c The main C source file
cache.c C functions for username/password caching
db.c C functions for username/password storage
AuthFilt.h AuthFilt header file
AuthFilt.htm AuthFilt Web page that uses AuthFilt filter for authentication.
MAKEFILE CTETest makefile for command line compilation

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Build and Install the Sample

To build this sample using the Visual C++ IDE, the following steps must be performed:

  1. Open the solution (VS.NET) or desktop (VS6) file to open the project.
  2. Click Build to create the DLL.

To build and run this sample without using the Visual C++ IDE, the following steps must be performed:

  1. Type NMAKE All from the command line. For example, if your sample files are located in a folder called C:\MySamples, type the following at the command line:
    cd /d c:\MySamples NMAKE All

 

To install this sample, the following steps must be performed:

  1. Copy the AuthFilt.dll and AuthFilt.htm files to a physical folder on your computer. For example, create a folder called C:\Samples and copy the files to that folder.
  2. Create a virtual directory that maps to the physical folder containing your files. To create a virtual directory, open the Internet Information Services (IIS) Manager by clicking Start, Run, type inetmgr in the text box and click OK. Right-click on the Web site where you want to create a virtual directory, click New, and click Virtual Directory. In the Alias text box, type the name you want for your virtual directory, for example, AuthFilt. In the Directory text box, type the path to the folder that contains your files.
  3. Install AuthFilt.dll as a filter on the Web site that contains your new virtual directory. In the IIS Manager, right-click the Web site, click Properties, and click the ISAPI Filters tab. Click Add to open the Filter Properties window. Type AuthFilt in the Filter Name text box, and type the path to your filter in the Executable text box. Click OK to complete the installation of the filter.
  4. Create a user file, c:\inetsrv\userdb.txt, which contains the username/password pairs and the appropriate account the username/password should be mapped to. The format of the file is:
    User1:Password1, NTUser1:NTPassword1
    Where each line contains the user name and password that will be used to authenticate the user, a comma, and the NT Username and password.
  5. Configure strong security on your new virtual directory. Right-click the virtual directory name, click Properties, and click the Directory Security tab. Press F1 for tips on securing your virtual directory.
  6. Use Windows Explorer to set restricted access control on the sample .dll file in its physical folder. For more information, click Start, Help and Support, and search for Access Control.
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Run the Sample

In order to run this sample, follow the instructions listed below:

  1. Browse to your sample Web files in Internet Explorer (IE). For example, if your files are in a virtual directory called AuthFilt, type http://localhost/AuthFilt/AuthFilt.htm in the Address bar of IE.
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Sample Output

After performing step 1 in Run the Sample, you should be queried for authentication based on the data in the user file you created.

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Help Desk

If here you do not find answers to your questions, visit the Microsoft Help and Support Web site.

Problem Possible Solution
When building the dll, C++ returns a permissions error. Once you have called the dll from your web page, your system considers it a loaded dll. You must unload it to build it again, either by unloading the ASP application or deleting the dll from system32\dllcache.
When browsing to the dll, IE gives you a permissions error. The folder and virtual directory must have Execute permissions set on them.

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